Digital key telephone system and extension terminal device thereof

ABSTRACT

According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT)  2  or a standard telephone (STT)  4  as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals  2  and  4  as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU)  12 . A control unit (RCTU)  16  determines the called extension terminal on the basis of the detected caller ID and the information stored in the storage means, so the extension terminal receives the call from the digital key telephone interface unit (RDKU)  13  or a standard telephone interface unit (RSTU)  15.

TECHNICAL FIELD

[0001] The present invention relates to a digital key telephone systemprovided in a company or an office.

BACKGROUND ART

[0002] A digital key telephone system comprises a main unit connected toa public network or a private branch exchange and a plurality of digitalkey telephones connected to the extension lines of the main unit. Thedigital key telephone has a plurality of push button type keys. Whenthese keys are depressed, calling the public network or the privatebranch exchange, answering a call, and speech communication betweendigital key telephones are allowed. The main unit processes not only acontrol signal but also a speech communication signal as a digitalsignal and executes calling processing/call reception processing of eachdigital key telephone by a stored program control scheme and switchingprocessing by a time switch of the digital speech communication signal.

[0003] As one of analog communication networks provided in U.S.A.recently, there is a communication network for providing a servicecalled, e.g., “CLASS (Custom Local Area Signaling Service)”. Thecommunication network for providing the CLASS service can superposecalling line identification information on a call signal and transmit itto the called subscriber.

[0004] When the digital key telephone system is connected to such acommunication network, the main unit of the called digital key telephonesystem detects the first bell signal and then a modem signal. Whencalling line identification information is detected from the modemsignal, the calling line identification information is transferred fromthe main unit to the called key telephone and displayed on the liquidcrystal display device (LCD) of the key telephone. The user of the keytelephone can recognize the calling line before off-hook by checking thecalling line identification information displayed on the liquid crystaldisplay device.

[0005] Conventionally, however, as the main function of the digital keytelephone system using the calling line information notification servicein the analog communication network such as the CLASS service, only theabove-described calling line identification information display functionis realized. Therefore, a demand has arisen for realization of a new andeffective functional service using the CLASS service.

[0006] Another demand has arisen for expansion or realization of varioussupport functions associated with wiring installation, a function ofallowing a variety of call reception processing by adding a plurality ofextension numbers to the digital key telephones, and a function ofallowing a variety of communication processing operations using apersonal computer combined with the digital key telephones.

DISCLOSURE OF INVENTION

[0007] It is an object of the present invention to provide a digital keytelephone system capable of expanding or realizing various functions,e.g., realizing a more effective function using a calling lineinformation notification service in an analog communication network.

[0008] In order to achieve the above object, according to the presentinvention, there is provided a digital key telephone system connected,through an office line, to an analog communication network having afunction of transmitting a ringing signal including calling lineidentification information, accommodating a plurality of extension linesconnected to extension terminals, and having a function of switching andconnecting the office line to the plurality of extension lines or theextension lines to each other, comprising called party storage meansstoring information representing a correlation between a calling lineand a called extension terminal in advance. By detecting the callingline identification information included in the ringing signal arrivingfrom the analog communication network, the called extension terminal isdetermined on the basis of the detected calling line identificationinformation and the information stored in the storage means, and callreception processing for the extension terminal is performed.

[0009] When called parties are registered in advance in correspondencewith calling parties, an optimum extension terminal user can answer acall from a calling line. For example, a terminal for receiving andanswering a call can be can be appropriately selected such that a personin charge directly answers a call from an important client, and asecretary answers calls from other clients.

[0010] In the present invention, when call reception processing isperformed for the called extension terminal in response to arrival ofthe ringing signal, and the extension terminal does not answer the call,the calling line identification information detected from the ringingsignal is stored in correspondence with the called extension terminal.When an operation of requesting call back is performed in the extensionterminal which does not answer the call, call back processing isperformed for the calling line on the basis of the stored calling lineidentification information. The calling line identification informationis stored upon detecting restoration of the called office line duringcall reception processing.

[0011] If a call is received in the absence of the extension terminaluser, the user can perform call back without the dialing operation onlyby performing the call back request operation. For this reason, the useroperation associated with the call back operation can be simplified.

[0012] In the present invention, fault determination means using thecalling line identification information is arranged. A detection resultobtained when the calling line identification information included inthe ringing signal is detected by the calling line identificationinformation detection means is compared with that obtained when thecalling line identification information is passed through the callingline identification information detection means together with theredundant data and detected by the fault determination means. With thisoperation, when a reception fault of the ringing signal is generated,determination processing is separately performed for each of the officeline and the digital key telephone system.

[0013] With this arrangement, the fault occurrence position can bedetermined using the calling line identification information arrivingfrom the analog communication network. As a result, separate faultdetermination can be relatively easily and properly performed, so ameasure against the fault can be appropriately and quickly taken.

[0014] According to the present invention, there is also provided adigital key telephone system comprising an external communicationinterface with a plurality of serial communication ports for performingserial communication with external computer devices, and having afunction of receiving function setting information sent from theexternal computer device through the external communication interfaceand setting a function of the digital key telephone system in accordancewith the received function setting information, comprising functionsetting regulation means. While the function setting information isbeing received from an arbitrary one of the plurality of externalcomputer devices, message information representing that function settingis disabled is transmitted to another external computer device, which isgoing to perform the function setting operation, and displayed, therebyregulating the function setting operation in another external computerdevice.

[0015] With this arrangement, the plurality of external computer devicesare prevented from simultaneously performing function setting, socongestion of function setting processing from the plurality of externalcomputer devices can be prevented.

[0016] When functions with different contents are set by the pluralityof external computer devices, a function set by one of the externalcomputer devices is preferentially operated in accordance with apredetermined rule. With this arrangement, even when a plurality offunctions with inconsistent functions are set, the system can beprevented from erroneously operating.

[0017] In the present invention, the external communication interfacecomprises serial communication interface means for serially transmittinga digital signal to the external computer device, modem communicationinterface means for performing modem communication of a digital signalto the external computer device, and a switching circuit for switchingbetween the serial communication interface means and the modemcommunication interface means. A communication request input beforesignal transmission to the external computer device is detected, and theswitching circuit is controlled in accordance with the detection resultto allow signal transmission to the external computer device as theother party of communication.

[0018] With this arrangement, data can be transmitted/received evento/from an external computer device connected to a serial communicationinterface such as an RS232C or an external computer device connectedthrough a communication line such as an office line or extension line.

[0019] In the present invention, evaluation test control means forperforming an evaluation test of the digital key telephone system incooperation with the external computer device is arranged. In addition,the external communication interface comprises a first signal path fortransmitting a signal sent from the external computer device,transferring the signal to the evaluation test control means, andtransferring the signal looped back by the evaluation test control meansto the external computer device, and a second signal path for loopingback the signal sent from the external computer device to the externalcomputer device without transferring the signal to the evaluation testcontrol means. The first and second signal paths are switched by thetext control means.

[0020] With this arrangement, text data returned through the firstsignal path and that returned through the second signal path arecompared in the external computer device, thereby confirming whether thecontrol circuit in the digital key telephone system properly operates.

[0021] According to the present invention, there is also provided adigital key telephone system having an external communication interfacewith a plurality of serial communication ports connected to externalcomputer devices, wherein the external communication interface comprisesa table memory which stores, in advance, information representing arelationship between the number of serial communication ports connectedto external computer devices and transmission rates which can be set foreach serial communication port. Every time an external computer deviceis connected to one of the plurality of serial communication ports, atransmission rate is assigned to the serial communication port on thebasis of the information stored in the table memory such that a sum oftransmission rates of the plurality of serial communication ports is notmore than a predetermined total transmission capability.

[0022] In accordance with the number of external computer devicesconnected to the serial communication ports, the maximum transmissionrate can always be assigned to each external computer device within therange under the condition at that time. Therefore, data transmission canalways be performed by using the transmission capacity of the externalcommunication interface at maximum, so a high transmission capacityutilization efficiency can be maintained.

[0023] In the present invention, in mounting units or connectingextension terminals, the power factor of each of the mounted units andconnected extension terminals is detected, it is determined whether thesum value of the detected power factors of the units and extensionterminals falls within a prescribed value, and the determination resultis notified to a user. As the determination result notification means,when the sum value of the power factors of, e.g., extension terminalsexceeds the prescribed value, a warning is issued to the extensionterminal to be connected.

[0024] With this arrangement, even when the installer or the like is toerroneously connect a number of extension terminals beyond theprescribed power factor value, the installer is warned of it, soconnection of a number of extension terminals beyond the prescribedpower factor value can be prevented.

[0025] According to the present invention, there is also provided adigital key telephone system comprising a basic cabinet accommodating acontrol unit for switching/connection, and a plurality of extensioncabinets accommodating a plurality of interface units each having aninterface function to an office line and extension lines, the extensioncabinets being stacked on the basic cabinet and connected to each otherthrough a connection cable, wherein each extension cabinet comprisesstacking position recognition means for recognizing a stacking positionof a self frame on the basis of a predetermined signal sent from thebasic cabinet. In accordance with the stacking position recognized bythe stacking position recognition means, channel conversion between aninterframe transmission channel for performing signal transmission tothe basic cabinet and an intraframe transmission channel for performingsignal transmission to each interface unit in the self frame isperformed.

[0026] With this arrangement, transmission channel conversion processingis performed in accordance with the stacking position of each extensioncabinet. That is, each extension cabinet can autonomously switch thechannel at any stacking position. Since the extension cabinets can havea common arrangement, manufacturing of extension cabinets can besimplified, and the cost can be reduced by the mass production effect,as compared to the manufacture of a dedicated extension cabinet at eachstacking position.

[0027] In the present invention, digital level conversion means forconverting an input signal level of each time slot into a differentsignal level and outputting the signal to a time switch for switchingand connecting the office line, the extension lines, and a tonegenerator, and level control means are arranged. In sending a tonesignal from the tone generator to the office line or the plurality ofextension lines, the gain of the digital level conversion means ischanged in accordance with the state of the office line or extensionline to which the signal is to be sent.

[0028] As a result, even when the tone signal is to be sent to aplurality of parties, the tone signal generated by one tone signalgenerator can be changed in level and sent in accordance with thedestination. Since a plurality of tone signal generators for generatingtone signals of different levels need not be arranged, the cost of thesystem can be reduced, and the reliability can be improved.

[0029] In the present invention, when the system has a camp-on functionof, if a new call arrives at an extension line which is communicating,sending a camp-on tone from the main unit to the extension line which iscommunicating to notify the call reception, the camp-on tone is changeddepending on whether the line at which the call arrives is the officeline or the extension line.

[0030] When another call addressed to the extension terminal duringcommunication is received, the user of the called extension terminal canidentify the calling line, i.e., the office line or extension line, fromthe difference in camp-on tone, so the user can appropriately answer thecall in accordance with the calling line.

[0031] As means for outputting the camp-on tone from the terminal, firstmeans for a digital key telephone and second means for a standardtelephone are selectively used. When the called terminal is a digitalkey telephone, the main unit sends a command for instructing generationof a camp-on tone and the type of the camp-on tone because the digitalkey telephone has a sound source for generating the tone. Upon receivingthe command, the digital key telephone generates a camp-on tone of thedesignated type from the sound source and outputs the camp-on tone. Tothe contrary, when the called terminal is a standard telephone, the mainunit generates the camp-on tone by itself because the standard telephonehas no tone source. The camp-on tone is mixed or inserted into thereception signal and sent to the standard telephone.

[0032] With this arrangement, the camp-on tone can be generatedindependently of the terminal, i.e., the digital key telephone or thestandard telephone.

[0033] In the present invention, when a directory number is assigned toeach extension terminal, and a directory number retrieval operation isperformed in the extension terminal in a predetermined procedure, thedirectory number assigned to the extension terminal is read out fromdirectory storage means and transmitted to the extension terminal whichhas performed the directory number retrieval operation to display thedirectory number.

[0034] With this arrangement, even when the user does not know orforgets the directory number of the self extension terminal, thedirectory number can be easily confirmed, as needed.

[0035] According to the present invention, there is also provided adigital key telephone system comprising a main unit connected to acommunication network through an office line, accommodating a pluralityof extension lines, and having at least a function of switching andconnecting the office line to the plurality of extension lines or theextension lines to each other, and a plurality of extension terminalsconnected to the plurality of extension lines of the main unit, whereinwhen a request for knowing the contents of an incoming call is sent fromone of the plurality of extension terminals, where the incoming callwaiting for call reception processing is present, the main unit suppliescall reception information representing the contents of the incomingcall waiting for call reception processing to the extension terminal ofthe request source in accordance with the request.

[0036] With this arrangement, when a plurality of incoming calls aresimultaneously addressed to the self extension terminal, the user canconfirm the contents of these incoming calls and answer the calls in thedescending order of degrees of importance. When a new incoming call isreceived during speech communication, the contents of the incoming callare confirmed while continuing speech communication. If the userdetermines that the new call is more important, the call during speechcommunication is held or ended. The user can immediately answer theimportant incoming call.

[0037] As a specific arrangement for realizing the call receptioninformation notification function, a request for knowing the contents ofthe incoming call is sent from the digital key telephone, and the callreception information sent from the main unit is displayed on thedigital key telephone. Alternatively, a computer device is connected tothe digital key telephone through an interface. A request for knowingthe contents of the incoming call is sent from the computer device, andthe call reception information sent from the main unit is displayed onthe computer device.

[0038] As means for sending the request for knowing the contents of theincoming call addressed to the self terminal, the request is transmittedevery time a request operation is performed by a user, or the request isautomatically transmitted at a predetermined timing.

[0039] When a plurality of incoming calls are addressed to one extensionterminal, and every time a request for knowing contents of an incomingcall is sent from the extension terminal, call reception information ofone of the plurality of incoming calls is sequentially selected andsupplied. Alternatively, pieces of information of all of the pluralityof incoming calls may be supplied in response to one request.

[0040] According to the present invention, there is also provided adigital key telephone system comprising call park control means for,when a call park request is input in an extension terminal which iscommunicating, holding a call to the extension terminal incorrespondence with an orbit number, and in this state, when anotherextension terminal accesses the orbit number, connecting the extensionterminal to the held call, wherein the call park control means holds theorbit number until the call is ended in holding the call subjected tocall park in correspondence with the orbit number, and when a reparkrequest for the call is generated while the call is continuouslyreceived, the call is held in correspondence with the orbit number atwhich the call is being held.

[0041] With this arrangement, when a repark request is generated, thecall to be subjected to call park at this time is held in correspondencewith the same orbit number as that in the preceding call park. For thisreason, a call is prevented from being held in correspondence withdifferent orbit numbers.

[0042] According to the present invention, there is also provided adigital key telephone system having a computer connection interface inat least one of extension terminals wherein an operation mode changerequest sent from a computer is transferred to a main unit through thecomputer connection interface, the main unit determines whether thetransferred mode change request is appropriate and supplies thedetermination result to the computer connection interface which hastransferred to the mode change request, and the computer connectioninterface comprises performs mode change processing in response to themode change request from the computer on the basis of the supplieddetermination result.

[0043] With this arrangement, when a mode change request is issued fromthe computer, the main unit always determines whether the request isappropriate. Only when it is determined that the request is appropriate,the computer connection interface performs mode change setting.Therefore, the computer connection interface can prevented from beingset in a mode which is not prepared in the main unit.

[0044] For example, assume that the user sends a request for changingthe mode to a computer telephoni mode from the computer to the computerconnection interface to send a call using the computer. If the main unitdoes not have the computer telephoni mode, the main unit returns no modechange enable notification. For this reason, the computer telephoni modeis not set for the computer connection interface. Even for anappropriate mode change request, when the operation state in the mainunit cannot currently cope with the mode change, the main unit returnsno mode change enable notification.

[0045] According to the present invention, there is also provided adigital key telephone system having a plurality of line selection keys,in an extension terminal, each of which corresponds to the office lineor extension line, wherein when the office line or the extension linecorresponding to one of the plurality of line selection key is held, andin this state, a request for displaying information associated with theheld office line or extension line is input in an extension terminal,the information associated with the held office line or extension lineis selectively displayed on the extension terminal in accordance withthe display request, and synchronized with the display operation,information representing the line selection key corresponding to theheld office line or extension line is displayed.

[0046] As the means for displaying the information representing the lineselection key, an indication lamp such as an LED provided incorrespondence with the line selection key is turned on, or the numberof the line selection key is displayed on a display device such as anLCD in correspondence with the number of the held line.

[0047] Display control of the information representing the held line andthe information representing the line selection key can be performed bythe main unit or the extension terminal device.

[0048] With this arrangement, the information associated with the heldoffice line or extension line and the information representing the lineselection key corresponding to the office line or extension line aredisplayed in correspondence with each other. For this reason, the usercan always properly recognize the line selection key corresponding tothe held line.

[0049] This arrangement is especially effective when a plurality ofdirectory numbers are added to one extension terminal. When a pluralityof lines with different directory numbers are being held, the userperforms the display operation to, e.g., scroll the pieces ofinformation of the held lines. Unless the user memorizes thecorrespondence between the pieces of displayed line information and theline selection keys, the user cannot know it. However, in the presentinvention, in synchronization with the scroll operation, the informationof a line selection key corresponding to the displayed line isdisplayed, and the user can properly know the correspondence between thedisplayed line information and the line selection key.

BRIEF DESCRIPTION OF DRAWINGS

[0050]FIG. 1 is a view showing the outer appearance of a digital keytelephone system according to an embodiment of the present invention;

[0051]FIG. 2 is a block diagram showing the arrangement of a main unitin the system shown in FIG. 1;

[0052]FIG. 3 is a circuit diagram showing the arrangement of an RCOU inthe main unit shown in FIG. 2;

[0053]FIG. 4 is a circuit diagram showing the arrangement of an RCIU inthe main unit shown in FIG. 2;

[0054]FIG. 5 is a circuit diagram showing the arrangement of an RDKU inthe main unit shown in FIG. 2;

[0055]FIG. 6 is a circuit diagram showing the arrangement of an RSTU inthe main unit shown in FIG. 2;

[0056]FIG. 7 is a circuit diagram showing the arrangement of an RSIU inthe main unit shown in FIG. 2;

[0057]FIG. 8 is a circuit diagram showing the arrangement of an RCTU inthe main unit shown in FIG. 2;

[0058]FIG. 9 is a block diagram showing the arrangement of a time switchsection in the RCTU shown in FIG. 8;

[0059]FIG. 10 is a plan view showing the outer appearance of a digitalkey telephone;

[0060]FIG. 11 is a block diagram showing the circuit arrangement of thedigital key telephone;

[0061]FIG. 12 is a block diagram showing the arrangement of an interfacecircuit section in the digital key telephone having a PCI-DI;

[0062]FIG. 13 is a timing chart showing a caller ID reception operation;

[0063]FIG. 14 is a flow chart showing the procedure and contents of callreception sound generation control using the caller ID;

[0064]FIG. 15 is a view showing a table memory storing the correlationbetween calling line numbers and sound generation telephone numbers;

[0065]FIG. 16 is a view showing an example of display of CLASSinformation on the digital key telephone;

[0066]FIG. 17 is a view showing an example of display of CLASSinformation in a repeater;

[0067]FIG. 18 is a flow chart showing the procedure and contents of callback control;

[0068]FIG. 19 show views of the sequence of switching a mode oftransmitting the caller ID from the RCIU to the RCTU;

[0069]FIG. 20 is a flow chart showing the procedure and contents offunction setting determination processing upon powering on;

[0070]FIG. 21 is a flow chart showing the procedure and contents ofdetermination processing when function setting is performed during theoperation of the system;

[0071]FIG. 22 is a view for explaining a state wherein an RS232Cinterface connection mode is set for the RSIU;

[0072]FIG. 23 is a view for explaining a state wherein a connection modeusing a modem interface is set for the RSIU;

[0073]FIG. 24 is a view for explaining a state wherein a connection modeusing a modem interface is set for the RSIU;

[0074]FIG. 25 is a table showing the correlation between the number ofports in use and the data transmission rate in the RSIU;

[0075]FIG. 26 is a table showing the correlation between the use purposeof a serial communication port and the communication scheme;

[0076]FIG. 27 is a view showing the connection structure between a basiccabinet and extension cabinets;

[0077]FIG. 28 is a block diagram showing the arrangement of a connectioninterface circuit between a basic cabinet 1 a and extension cabinets 1b;

[0078]FIG. 29 is a table showing the correlation between each extensioncabinet, a cabinet position recognition signal, and a data channelswitching signal;

[0079]FIG. 30 is a circuit diagram showing the circuit arrangement of acabinet position recognition circuit;

[0080]FIG. 31 is a table showing the correlation betweenbasic-cabinet-side data and extension-cabinet-side data in a downwardlink switching circuit of each extension cabinet;

[0081]FIG. 32 is a circuit diagram showing the arrangement of thedownward link switching circuit;

[0082]FIG. 33 is a table showing the correlation between thebasic-cabinet-side data and the extension-cabinet-side data in an upwardlink switching circuit of each extension cabinet;

[0083]FIG. 34 is a circuit diagram showing the arrangement of the upwardlink switching circuit;

[0084]FIG. 35 is a view showing the correlation between each extensioncabinet and the number of channels of downward link data from the basiccabinet;

[0085]FIG. 36 is a view showing control data output from a connectionmemory;

[0086]FIG. 37A is a view for explaining the first use example of adigital attenuator arranged in a time switch section;

[0087]FIG. 37B is a view for explaining the second use example of thedigital attenuator arranged in the time switch section;

[0088]FIG. 37C is a view for explaining the third use example of thedigital attenuator arranged in the time switch section;

[0089]FIG. 38A is a view showing a display example upon depressing adirectory key;

[0090]FIG. 38B is a view showing a display example upon inputting adirectory number;

[0091]FIG. 38C is a view showing a display example upon inputting anextension number;

[0092]FIG. 39A is a view showing the first operation and display exampleassociated with an inquiry for a directory number;

[0093]FIG. 39B is a view showing the second operation and displayexample associated with an inquiry for a directory number;

[0094]FIG. 39C is a view showing the third operation and display exampleassociated with an inquiry for a directory number;

[0095]FIG. 39D is a view showing the fourth operation and displayexample associated with an inquiry for a directory number;

[0096]FIG. 40A is a flow chart showing the procedure and contents ofcall reception information storage control;

[0097]FIG. 40B is a flow chart showing the procedure and contents ofcall reception information display control;

[0098]FIG. 41 is a view showing an example of a park reservation tableto be used for call park;

[0099]FIG. 42 is a flow chart showing a call park control procedure bythe RCTU;

[0100]FIG. 43 is a flow chart showing a repark control procedure by theRCTU;

[0101]FIG. 44 is a flow chart showing a pickup control procedure by theRCTU;

[0102]FIG. 45 is a flow chart showing a mode change control procedure inthe PCI-DI and the RCTU of the main unit;

[0103]FIG. 46 is a flow chart showing a holding display controlprocedure;

[0104]FIG. 47 is a view showing an example of a holding informationarea;

[0105]FIG. 48 is a view showing an order of blinking LEDs correspondingto line selection keys;

[0106]FIG. 49 is a view showing an example of the arrangement of DNkeys;

[0107]FIG. 50 is a view schematically showing the first half of anextension operation using DNs;

[0108]FIG. 51 is a view schematically showing the second half of theextension operation using the DNs;

[0109]FIG. 52 is a view schematically showing an extension ring transferoperation using the DNs;

[0110]FIG. 53 is a view schematically showing an ACB operation using theDNs;

[0111]FIG. 54 is a view schematically showing an office line callingoperation and a ring transfer operation using the DNs;

[0112]FIG. 55 is a view schematically showing the first half of anoffice line calling operation and a conference operation using the DNs;

[0113]FIG. 56 is a view schematically showing the second half of theoffice line calling operation and the conference operation using theDNs;

[0114]FIG. 57 is a table showing an example of LED display of the DNkeys;

[0115]FIG. 58 is a table showing an operation performed when no DN isavailable or when no DN key is available;

[0116]FIG. 59 is a table showing an example of processing extension callreception during extension call reception using the DNs;

[0117]FIG. 60 is a table showing an example of DND processing duringcall reception;

[0118]FIG. 61 is a table showing a call forward operation using the DNs;

[0119]FIG. 62 is a view showing an operation performed when the CFdestination is a phantom DN;

[0120]FIG. 63 is a view showing an LCD display example of the CF when aplurality of CF destinations can be set from one terminal;

[0121]FIG. 64 is a view showing the correlation between phantom DNs andMW keys;

[0122]FIG. 65 is a view showing an LCD display example upon receivingmessage waiting;

[0123]FIG. 66 is a view showing an LCD display example upon transmittingmessage waiting;

[0124]FIG. 67 is a view showing an operation of receiving messagewaiting to a primary DN;

[0125]FIG. 68 is a view showing an operation of receiving messagewaiting to a phantom DN;

[0126]FIG. 69 is a view showing another operation of receiving messagewaiting to a phantom DN;

[0127]FIG. 70 is a view showing an operation of transmitting messagewaiting from a primary DN;

[0128]FIG. 71 is a view showing an operation of transmitting messagewaiting from a secondary DN;

[0129]FIG. 72 is a view showing an operation of transmitting messagewaiting from a phantom DN;

[0130]FIG. 73 is a view showing an ID sending operation to a voice mailin message waiting;

[0131]FIG. 74 is a view showing the ID sending operation of a voice mailin call forward;

[0132]FIG. 75 is a view showing a Buzz key operation;

[0133]FIG. 76 is a view showing the LED ON timing of a Buzz keyoperation terminal, the LED ON timing of a Buzz called terminal, and anMSG tone generation pattern;

[0134]FIG. 77 is a table showing the display example of office lineLEDs;

[0135]FIG. 78 is a table showing patterns of a display operation when“I-Called” is displayed for a primary line;

[0136]FIG. 79 is a table showing patterns of a display operation whencall reception display is performed on a designated DN independently ofthe presence/absence of a CO key upon receiving a call;

[0137]FIG. 80 is a table showing the summary of operations in the busystate;

[0138]FIG. 81 is a timing chart showing a delay call reception operationin ring transfer for an extension HFU calling destination;

[0139]FIG. 82 is a timing chart showing the delay call receptionoperation in ring transfer for an extension tone calling destination;

[0140]FIG. 83 is a timing chart when an on-hook operation is performedduring a tone calling delay operation;

[0141]FIG. 84 is a view showing an example of a speech communicationmanagement record printed by an SMDR;

[0142]FIG. 85 is a view showing a DN call reception operation by anavailable DN;

[0143]FIG. 86 is a view showing the DN call reception operation duringcall reception when a DN is available;

[0144]FIG. 87 is a view showing an operation of the DN key during callreception;

[0145]FIG. 88 is a view showing the DN call reception operation duringspeech communication;

[0146]FIG. 89 is a view showing the DN call reception operation duringspeech communication when a DN is available;

[0147]FIG. 90 is a view showing the DN call reception operation duringspeech communication when no DN is available;

[0148]FIG. 91 is a view showing the transmission format of calling lineidentification information sent from a public network using a CLASSservice;

[0149]FIG. 92 is a flow chart showing the procedure and contents of awiring mode start control;

[0150]FIG. 93 is a flow chart showing the procedure and contents of awiring mode end control;

[0151]FIG. 94 is a table showing the correlation between operationsusing the DN keys and displayed symbols;

[0152]FIG. 95 is a view for explaining an extension speech communicationoperation using the DN keys;

[0153]FIG. 96 is a view for explaining a CF destination DN settingoperation using a primary DN key;

[0154]FIG. 97 is a view for explaining the CF destination DN settingoperation using a phantom DN key;

[0155]FIG. 98 is a view for explaining a voice mail ID code settingoperation using the primary DN key;

[0156]FIG. 99 is a view for explaining the voice mail ID code settingoperation using the phantom DN key;

[0157]FIG. 100 is a flow chart showing the procedure and contents of DNnumber display control;

[0158]FIG. 101 is a view showing an example of the connection DN areamap in a RAM;

[0159]FIG. 102 is a view for explaining the procedure of functionsetting for keys of the DKT/EKT;

[0160]FIG. 103 is a view showing an example of the key arrangement areamap in the DKT/EKT;

[0161]FIG. 104 is a flow chart showing the procedure and contents ofcamp-on tone sending control;

[0162]FIG. 105A is a chart showing the signal waveform of an office linecamp-on tone generated by the DKT/EKT;

[0163]FIG. 105B is a chart showing the signal waveform of an extensioncamp-on tone generated by the DKT/EKT;

[0164]FIG. 105C is a chart showing the signal waveform of an office linecamp-on tone generated by a standard telephone; and

[0165]FIG. 105D is a chart showing the signal waveform of an extensioncamp-on tone generated by the standard telephone.

BEST MODE OF CARRYING OUT THE INVENTION

[0166]FIG. 91 is a view showing a signal format used in a communicationnetwork using a CLASS service. A modem signal is inserted into theinterval between the first bell signal and the second bell signal of aringing signal. This modem signal has a format in which a synchronoussignal consisting of a repetitive pattern of “01” is arranged at thestart position, a mark signal, a message type word, a data word count,and a data portion sequentially follow the synchronous signal, and achecksum is arranged at the last position. Calling line identificationinformation is inserted into the data portion. The calling lineidentification information contains “time”, i.e., date and time,“calling line ID”, “reason for absence of DN”, “name”, and “reason forabsence of name”.

[0167]FIG. 1 is a view showing the outer appearance of a digital keytelephone system according to an embodiment of the present invention.

[0168] This system comprises a main unit (KSU) 1 connected to an analogpublic network (PSTN) (not shown) through a subscriber line (CO line),digital key telephones (DKTS) 2 connected to the extension lines asextension terminals, a personal computer (PC) 3, a standard telephone(STT) 4, a personal computer (PC) 6 connected to the main unit 1 througha modem 5 as an external device, a communication information managementunit (MIS) 7 for accumulating/managing communication information, and acommunication management recording unit (SMDR) 8 for printing acommunication management record or the like.

[0169] The main unit 1 is constituted by stacking one basic cabinet 1 aand a plurality of (five in FIG. 1) extension cabinets 1 b. The basiccabinet 1 a and the extension cabinets 1 b are connected through datacables (not shown). The basic cabinet 1 a mainly incorporates a controlunit in addition to a power supply unit. Each extension cabinet 1 bmainly incorporates various interface units in addition to a powersupply unit. Each unit has a card shape and is inserted into a slot onthe mother board of each frame.

[0170]FIG. 2 is a block diagram showing the arrangement of the main unit1.

[0171] The main unit 1 comprises an office line interface 11 (RCOU), acalling line identification information interface unit (RCIU) 12, adigital key telephone interface unit (RDKU) 13, a serial communicationcontrol unit (RSIU) 14, a standard telephone interface unit (RSTU) 15,and a control unit (RCTU) 16. The interface units 11 to 15 are connectedto the control unit 16 through a data highway 17 and a PCM highway 18.The data highway 17 is used to perform control data transfer between theunits. The PCM highway 18 is used to transmit a digital speechcommunication signal between the units.

[0172] The office line interface 11 of the main unit 1 also has a leasedline, a private branch exchange (PBX), and an interface (not shown)connected to another key telephone system.

[0173] The central office line interface unit (RCOU) 11 performs anoffice line interface operation for an analog public network NW, e.g.,call reception detection, polarity inversion detection, opening/closingof a DC loop, dial sending, or the like under the control of the controlunit 16, and also performs processing of converting an analog speechsignal arriving via the subscriber line (CO line) into a PCM signal orprocessing of converting a PCM signal transferred from the control unit16 into an analog speech signal and sending the speech signal to thesubscriber line.

[0174]FIG. 3 is a circuit diagram showing the arrangement of the RCOU11. As shown in FIG. 3, the RCOU 11 comprises an interface circuit 110,a codec section 111, a time slot assigner 112, and a control datacommunication microcomputer 113. The interface circuit 110 has a callreception detection circuit 110 a connected to the subscriber line, apolarity inversion circuit 110 b, and a DC loop circuit 110 c. The callreception detection circuit 110 a detects a call signal arriving fromthe analog public network NW via the subscriber line. The polarityinversion circuit 110 b detects polarity inversion which occurs on thesubscriber line during the call connection process. The DC loop circuit110 c closes the DC loop in calling, transmits a dial pulse, and opensthe DC loop at the end of speech communication.

[0175] The codec section 111 has an A/D converter and a D/A converter toperform PCM coding processing of converting a transmission speech signalinto PCM speech data and PCM decoding processing of converting receivedPCM speech data into an analog reception speech signal.

[0176] The time slot assigner 112 determines the timing of speech datatransmission between the codec section 111 and the PCM highway 18 on thebasis of a predetermined time slot address, and a frame synchronoussignal and clock signal from the PCM highway 18, and notifies the codecsection 111 of this timing. The codec section 111 transmits/receives PCMspeech data to/from the PCM highway 18 at the timing designated by thetime slot assigner 112.

[0177] The control data communication microcomputer 113 monitorsdetection signals from the call reception detection circuit 110 a andthe polarity inversion circuit 110 b and controls DC loopopening/closing and dial pulse transmission in the DC loop circuit 110c. The control data communication microcomputer 113 transmits/receivescontrol data associated with call reception detection, polarityinversion detection, DC loop opening/closing, and dial pulsetransmission to/from the control unit 16 through the control datahighway 17.

[0178] The calling line identification information interface unit (RCIU)12 interfacing to the subscriber line has an arrangement shown in FIG.4. The RCIU 12 comprises a relay 120, a demodulation circuit 121, aserial/parallel conversion section 122, a data detection signaltransmission section 123, a relay control section 124, a detection unitcontrol section 125, and a memory 126. The serial/parallel conversionsection 122, the data detection signal transmission section 123, therelay control section 124, and the memory 126 are connected to thedetection unit control section 125 through an internal data bus 127.

[0179] The demodulation circuit 121 receives a modulated signal(notification data) arriving from the analog public network NW throughthe subscriber line (CO line) and demodulates the signal to detectcalling line number identification information (caller ID). Theserial/parallel conversion section 122 converts the calling lineidentification information output from the demodulation circuit 121 as aserial signal into a parallel signal. The data detection signaltransmission section 123 sends the calling line identificationinformation output from the demodulation circuit 121 to the internaldata bus 127. This notification data is transferred from the detectionunit control section 125 to the control unit 16 through the data highway17.

[0180] The relay 120 is used to disconnect the RCIU 12 from thesubscriber line. The relay control section 124 controls the relay 120 todisconnect the RCIU 12 from the subscriber line and match the impedancein dial sending or speech communication.

[0181] The detection unit control section 125 controls the calling linenumber detection unit 12. The memory 126 is used as an external storagesection of the detection unit control section 125.

[0182]FIG. 4 shows only one set of units. When a plurality of CO linesare led to the main unit 1, the relay 120, the demodulation circuit 121,the serial/parallel conversion section 122, the data detection signaltransmission section 123, and the relay control section 124 of the abovecircuits are arranged in units of CO lines. That is, the RCIU 12incorporates circuits equal in number to the subscriber lines.

[0183] The digital key telephone interface unit (RDKU) 13 as aninterface between the main unit 1 and each digital key telephone (DKT) 2has an arrangement shown in FIG. 5.

[0184] The RDKU 13 has ping-pong transmission circuits 131 l to 131 ncorresponding to the number of extension lines. Each of the ping-pongtransmission circuits 131 l to 131 n performs ping-pong transmission ofspeech or information terminal data and control data between the RDKU 13and a corresponding one of the digital key telephones 2 by using a timedivision channel of a 2B+D scheme, i.e., having two B channels (B1 andB2) with a transmission rate of 64 kbps and one D channel with atransmission rate of 16 kbps. The ping-pong transmission circuit has a2B+D generation section and a 2B+D separation section.

[0185] The 2B+D generation section synthesizes speech data andinformation terminal data on downward link channels B1 and B2 from thePCM highway 18 and control data on a downward link channel D from acontrol data communication microcomputer 133 into a data packet with a2B+D format and transmits the data packet to each digital key telephone2. The 2B+D separation section separates an upward link data packetarriving from each digital key telephone 2 into speech and informationterminal data on the upward link channels B1 and B2 and control data onthe upward link channel D and transfers the data to the PCM highway 18and the control data communication microcomputer 133.

[0186] The channel B1 is assigned to speech data transmission to eachdigital key telephone 2 while the channel B2 is assigned to transmitinformation terminal data when an information terminal such as apersonal computer is connected to each digital key telephone 2.

[0187] A time slot assigner 132 receives a frame synchronous signal andclock signal from the PCM highway 18 and notifies the ping-pongtransmission circuits 131 l to 131 n of the timing fortransmitting/receiving upward and downward link data on the B channelto/from the PCM highway 18. Therefore, each of the ping-pongtransmission circuits 131 l to 131 n directly accesses the PCM highway18 at the timing designated by the time slot assigner 132 totransmit/receive upward and downward link data at a transmission rate of2.048 Mbps.

[0188] The control data communication microcomputer 133 monitors Dchannel data transmitted/received by the ping-pong transmission circuits131 l to 131 n and controls to transmit/receive the D channel datato/from the control unit 16 through the data highway 17.

[0189] The standard telephone interface unit (RSTU) 15 as an interfacebetween the main unit 1 and the standard telephone 4 has an arrangementshown in FIG. 6. The RSTU 15 comprises a call signal sending circuit150, a DC supply circuit 151, and a dial detection section 152. The callsignal sending circuit 150 sends a 16-Hz call signal generated by a callsignal generation source 156 to the standard telephone 4. The DC supplycircuit 151 has a function of detecting opening/closing the DC loopbetween the RSTU 15 and the standard telephone 4 and supplies thedetection signal to a microcomputer 157. The DC supply circuit 151 alsohas a function of feeding a prescribed DC voltage to the standardtelephone 4 when the DC loop is closed and inverting the polarity ofthis DC voltage under the control of the microcomputer 157. The dialdetection section 152 detects a dial pulse sent from the standardtelephone 4 and supplies the detection signal to the microcomputer 157.

[0190] The RSTU 15 also has a codec 154, and a time slot assigner 155for designating the operation timing of the codec 154. The codec 154receives a transmission speech signal sent from the standard telephone 4through a transducer 153, converts the speech signal into a PCM signal,and sends the PCM speech data to the PCM highway 18. The codec 154 alsoconverts speech data sent from the PCM highway 18 into an analog speechsignal and transmits the speech signal to the standard telephone 4through the transducer 153. The time slot assigner 155 determines thetiming of speech data transmission between the codec 154 and the PCMhighway 18 on the basis of a frame synchronous signal and clock signalfrom the PCM highway 18 and designates the timing for the codec 154.

[0191] The microcomputer 157 ON/OFF-controls a call signal to the callsignal sending circuit 150, monitors DC loop opening/closing detectionand controls polarity inversion in the DC supply circuit 151, andmonitors dial pulse detection in the dial detection section 152. Themicrocomputer 157 also transmits/receives control data to/from thecontrol unit 16 through the data highway 17.

[0192] The serial communication control unit (RSIU) 14 for connecting anexternal information device such as a personal computer, thecommunication management recording unit (SMDR) 8, and a printer 9 to themain unit 1 has an arrangement shown in FIG. 7. The RSIU 14 has aplurality of (four in FIG. 7) serial communication ports 1410 to 1413and a control section 140. Of the serial communication ports 1410 to1413, the serial communication port 1410 has only an RS232Cdriver/receiver (D/R) and is directly connected to the serial I/O of thecontrol section 140. Each of the serial communication ports 1411 and1412 has an RS232C driver/receiver (D/R) 141 b and an asynchronoustransfer circuit (UART: Universal Asynchronous Receiver Transmitter) 141a and connects an external information device to a CPU bus 143 of thecontrol section 140 to transfer data.

[0193] The serial communication port 1413 has not only an RS232Cinterface function but also a modem interface function. The serialcommunication port 1413 has a modem 141 c, a codec 141 d, and aswitching circuit 141 e in addition to the RS232C driver/receiver 141 band the UART 141 a. The modem 141 c and the codec 141 d are used fordata transmission between the RSIU 14 and the PCM highway 18. Theswitching circuit 141 e switches connection between the UART 141 a, theRS232C driver/receiver 141 b, and the modem 141 c in accordance with aswitching control signal from the control section 140.

[0194] The control section 140 is constituted by a one-chip CPU andtransmits/receives control data to/from the control unit 16 through theCPU bus 143 having a dual port RAM 144. The control section 140 alsocontrols to transfer communication data transmitted/received by theserial communication ports 1410 to 1413 to another unit in the main unit1.

[0195] The control unit (RCTU) 16 for systematically controlling theoperation of the main unit 1 has an arrangement shown in FIG. 8. Thecontrol unit 16 has a main CPU 161 constituted by a microprocessor. Thismain CPU 161 is connected to a ROM 162, a RAM 163, a local CPU 164, anda time switch section 165 through a bus 168.

[0196] The ROM 162 stores various programs or control data necessary forswitching control in advance. The RAM 163 is used to store maintenancedata, user data, or control data generated in various control processes.The local CPU 164 controls control data transfer between the main CPU161 and the data highway 17.

[0197] The control unit 16 also has a tone data ROM 166 and aparallel/serial conversion circuit (P/S) 167. The tone data ROM 166reads out tone data representing a tone signal to be supplied to thedigital key telephones 2 and standard telephone 4 as extension terminalsin accordance with an instruction from the main CPU 161 during variousservices such as holding, transfer, or camp-on. The parallel/serialconversion circuit 167 converts the tone data read out from the tonedata ROM 166 as a parallel signal into a serial signal and sends thesignal to the data highway 17.

[0198] The time switch section 165 performs time slot switchingprocessing between an upward link PCM highway 18 a and a downward linkPCM highway 18 b under the control of the main CPU 161.

[0199]FIG. 9 is a block diagram showing the arrangement of the timeswitch section 165. The time switch section 165 comprises aserial/parallel converter (S/P) 1651, a data memory 1652, a digitalattenuator section 1653, a multiplexer (MUX) 1654, and a parallel/serialconverter (P/S) 1655. The time switch section 165 also comprises acontrol register 1656, a connection memory 1657, and a frame counter1658.

[0200] Each time slot data transferred by the upward link PCM highway 18a is converted from the serial signal into a parallel signal by the S/P1651, temporarily stored in the data memory 1652, and then input to thedigital attenuator section 1653. The digital attenuator section 1653 haseight attenuators from −18 dB to +3 dB. Every time slot data is inputfrom the data memory 1652, one of the attenuators is activated inaccordance with control data output from the connection memory 1657. Theinput time slot data is gain-controlled by the activated attenuator andoutput.

[0201] The multiplexer 1654 shifts the time slot data output from thedigital attenuator section 1653 to the time slot of the downward linkPCM highway 18 b in accordance with an instruction from the connectionmemory 1657. The time slot data output from the multiplexer 1654 isconverted from the parallel signal into a serial signal by theparallel/serial converter (P/S) 1655 and sent to the downward link PCMhighway 18 b.

[0202] The frame counter 1658 generates a signal necessary for theoperation of the time switch section 165 on the basis of a clock signalgenerated by a timing generation section (not shown) and a frame signalfrom the PCM highway 18.

[0203] Each of the digital key telephones 2 has the followingarrangement. FIG. 10 is a plan view showing the outer appearance of thedigital key telephone 2. FIG. 11 is a block diagram showing the circuitarrangement of the digital key telephone 2.

[0204] Referring to FIG. 10, a handset 22 is mounted on the cradleportion of a telephone body 21. The operation panel of the telephonebody 21 has dial buttons 23, a plurality of flexible buttons 24, aplurality of LED display devices 25 respectively corresponding to theflexible buttons 24, a plurality of control buttons 26, LED displaydevices 27 each corresponding to a predetermined control button, and anLED display device 28.

[0205] Of the above operation buttons, the flexible buttons 24 are usedby the user to freely set various functions such as an office linecalling or automatic dialing. Examples of functions to be set other thanoffice line calling are leased line calling, automatic dialing, pause,long pause, automatic redialing, saving, subaddress sending, dialsending, privacy cancel, messaging, message switching, message waiting,night switching, call reception rejection, absence transfer, fixedabsence transfer, camp-on, pooling, park holding, call pickup, callanswering, broadcasting, microphone-off, hot line, andconference/transfer.

[0206] Leased line calling is used for calling in communication betweenterminals connected to an intra-office communication network.

[0207] For automatic dialing, the telephone numbers of parties to becalled are registered in a memory in advance in correspondence with theflexible buttons. Depressing a flexible button allows automatic callingto the corresponding called party.

[0208] Pause is a function of inserting a pause between, e.g., an officeline calling dial number and a called party dial number in abbreviateddialing registration. Long pause is a function of inserting a longerpause.

[0209] Automatic redialing is a function of automatically repeatingredialing when the called party is busy.

[0210] In saving, in a period from the end of the dialing operation tothe end of the speech communication, a flexible button for which thesave function is set is depressed to temporary store the dial number ofthe called party. After the speech communication is complete, automaticcalling to the same called party is allowed by depressing the flexiblebutton for which the save function is set.

[0211] Subaddress sending is a function used to designate one of aplurality of communication terminal devices connected to one digitalline on the side of the other communication party connected to the ISDN.

[0212] In dial sending, the dial number and subaddress of the calledparty are input and then sent in calling to the ISDN.

[0213] Call reception rejection is a function of rejecting a call fromanother extension line. When an extension terminal for which callreception rejection is set is called, a busy tone with a period shorterthan that of a normal busy tone is returned.

[0214] Messaging is a function of registering a message for absenceanswering in advance and sending the message to the calling line uponreceiving a call in absence of the called party. Message switching is afunction of selecting one of a plurality of messages recorded in advancefor absence answering.

[0215] Message waiting is a function of causing the called terminal todisplay a message by designating it on the calling side when the calledparty is busy or absent.

[0216] Night switching is a function of switching between extensionterminals for receiving a call in the daytime or weekdays and those forreceiving a call in the nighttime or holidays.

[0217] Absence transfer or fixed absence transfer is a function ofregistering the extension number of a transfer destination in advance,and when a call is received in the absence transfer mode, automaticallytransferring the call to the transfer destination. Absence transfer andfixed absence transfer are different in the following points. In absencetransfer, the user can register or cancel the desired transferdestination anytime. In fixed absence transfer, once the transferdestination is set at the time of installation, it cannot be changedlater. Transfer destination setting for absence transfer can be made notonly from the extension terminal as the transfer source but also fromanother extension terminal.

[0218] In camp-on, when a called extension terminal or office lineterminal is busy, the calling terminal sets camp-on and goes on-hook.After the called terminal completes speech communication, the callingterminal is notified of it. The calling terminal automatically calls thecalled terminal upon off-hook. When the called terminal answers thecall, the called terminal and the calling terminal are connected toallow speech communication.

[0219] In pooling, a number of accommodated office lines are dividedinto groups, and each group is assigned to a pool. By designating onepool, all office lines of the group assigned to the pool can beselectively used. This function is effectively used when there are a lotof office lines, and they cannot be individually assigned to theflexible buttons. Park holding is a function used to hold speechcommunication by using the pool. Holding using no pool is performed bydepressing a holding button.

[0220] Call pickup or call answering is a function of answering anoffice line call in an extension terminal by a one-touch or specialnumber operation when nobody answers the call. Call pickup and callanswering are different in the following points. In call pickup, alloffice line calls can be answered. In call answering, however, aplurality of office lines are divided into groups, and the callanswering function is set for different flexible buttons in units ofgroups, thereby allowing call answering for each group.

[0221] Broadcasting is a function of voice-calling all extensionterminals or the extension terminals of a group. The microphone-offfunction is used when the called party does not want to answer by voicein broadcasting or group call. In this case, the microphone forloudspeaking speech communication is turned off.

[0222] Privacy cancel is a function of adding a third party to speechcommunication by a one-touch operation during office line speechcommunication to allow conference speech communication.

[0223] Hot line is a function of calling a desired extension terminal bya one-touch operation. During office line speech communication, bydepressing a flexible button for which the hot line function is set, thecall can be transferred by voice (call transfer) or a transfer tone(ring transfer). By depressing a flexible button for whichconference/transfer is set when the transfer destination party answersthe call, the mode changes to an office line conference mode. When theflexible button for which the hot line is set is depressed duringextension speech communication, the extension speech communication isheld. By depressing the flexible button for which conference/transfer isset when the other party of extension hot line answers the call, themode changes to the extension conference mode. When the handset goeson-hook in the extension conference mode, the extension call istransferred.

[0224] Each of the digital key telephones 2 is constituted by a speechcommunication circuit 200 and a control circuit 220, as shown in FIG.11.

[0225] Each of the digital key telephones 2 has, as speech communicationmodes, a handset speech communication mode using the handset 22 and ahands-free speech communication using a hands-free loudspeaker 212 and ahands-free microphone 213.

[0226] When the handset speech communication mode is selected, atransmission signal output from the microphone of the handset 22 isinput to a codec 203 through a transmission amplifier 207 and a channelswitch 208. When the hands-free speech communication is selected, atransmission signal output from the hands-free microphone 213 is inputto the codec 203 through a transmission amplifier 214 and a channelswitch 215.

[0227] The codec 203 converts the input transmission signal into speechcommunication data by PCM coding and supplies the speech communicationdata to a ping-pong transmission circuit 202 as B1 channel data. Theping-pong transmission circuit 202 has a 2B+D synthesis section. The2B+D synthesis section synthesizes the B1 channel speech communicationdata with D channel control data output from a speech communicationcontrol microcomputer 221 (to be described later) to generate upwardlink transmission data having the 2B+D format. This transmission data issent to the RDKU 13 through a transducer 201.

[0228] Downward link transmission data having the 2B+D format, whicharrives from the RDKU 13, is input to the ping-pong transmission circuit202 through the transducer 201. The ping-pong transmission circuit 202has a 2B+D separation section. The 2B+D separation section performsprocessing of separating the downward link transmission data into B1 andB2 channel speech communication data and D channel control data. The B1channel speech communication data is supplied to the codec 203. The Dchannel control data is supplied to the speech communication controlmicrocomputer 221.

[0229] The codec 203 performs signal processing of PCM-decoding the B1channel speech communication data to reproduce the reception signal. Inthe handset speech communication mode, the reception signal is suppliedto the loudspeaker of the handset 22 through a channel switch 204, anattenuator 205, and a reception amplifier 206. In the hands-free mode,the reception signal is supplied to the hands-free loudspeaker 212through a channel switch 209, an attenuator 210, and a receptionamplifier 211 and output from the loudspeaker 212.

[0230] The control circuit 220 has the speech communication controlmicrocomputer 221. The speech communication control computer 221systematically performs all control operations associated with speechcommunication while transmitting/receiving control data to/from the mainunit 1. The control contents include an operation of detecting theoperation information of the dial buttons 23, the flexible buttons 24,the control buttons 26, and a hook switch 222, OF/OFF-control of theplurality of LED display devices 25 and 27, control of supplying displaydata to an LCD driving circuit 223 to cause the LED display device 28 todisplay it, selective ON/OFF-control of the channel switches 204, 208,209, and 215 in accordance with the speech communication mode, andcontrol of changing the attenuation amount of the attenuator 205 or 210in accordance with the operation amount of the volume control (notshown).

[0231] A digital key telephone having a PC interface unit (PCI-DI) 2 bhas the following arrangement. FIG. 12 is a block diagram showing thearrangement of the interface circuit.

[0232] The interface circuit comprises a telephone interface section 230and a computer interface section 240. The telephone interface section230 comprises a transducer 231, a ping-pong transmission circuit 232, aspeech communication control microcomputer 233, and a selector 234. Theping-pong transmission circuit 232 and the speech communication controlmicrocomputer 233 have almost the same functions as those of theping-pong transmission circuit 202 and the speech communication controlmicrocomputer 221 described above with reference to FIG. 11.

[0233] The selector 234 selects one of speech communication control dataoutput from the speech communication control microcomputer 233 and datacommunication control data output from a data communication controlmicrocomputer 245 (to be described later) and supplies the selected datato the ping-pong transmission circuit 232 as D channel data.

[0234] The computer interface section 240 has the following arrangement.

[0235] B2 channel downward link transmission data separated by theping-pong transmission circuit 232 is converted from the serial datainto parallel data by a serial/parallel converter (S/P) 241. The B2channel downward link transmission data has eight bits (64 kbps). Thesix bits of these eight bits are assigned to communication data RD (48kbps), and the remaining two bits are assigned to a reception carrierdetection signal CD (8 kbps) and a transmission enable signal CS (8kbps) of the RS232C interface, respectively.

[0236] In the 8-bit parallel data output from the S/P 241, the 6-bitreception data RD is converted into serial data by a parallel/serialconverter (P/S) 242 and then sent to the personal computer 3 through aselector 243 and an R232C driver/receiver 244. The reception carrierdetection signal CD and the transmission enable signal CS are sent tothe personal computer 3 through the driver/receiver 244 and also fetchedby the data communication control microcomputer 245.

[0237] Transmission data SD (48 kbps) sent from the personal computer 3is input to a serial/parallel converter (S/P) 246 through the RS232Cdriver/receiver 244 and a selector 248, converted into parallel data,and input to a parallel/serial converter (P/S) 247. Simultaneously, anRS232C interface transmission request signal RS (8 kbps) and thetransmission enable signal CS (8 kbps) which are sent from the personalcomputer 3 are input to the parallel/serial converter (P/S) 247.

[0238] For this reason, 8-bit serial data constituted by thetransmission data SD, the transmission request signal RS, and thetransmission enable signal CS is output from the P/S 247. This serialdata is supplied to the ping-pong transmission circuit 232 as B2 channelupward link transmission data. The ping-pong transmission circuit 232multiplexes it with the B1 channel upward link speech communication dataand D channel upward link control data and sends the data to the RDKU 13of the main unit 1.

[0239] The operation of the digital key telephone system having theabove arrangement will be described next.

[0240] (1) Various Operations Using Caller ID

[0241] (1-1) Reception and Call Reception Processing of Caller ID

[0242] A caller ID is received by the RCIU 12. The RCIU 12 checks thecaller ID transmitted from the analog public network NW. Upon confirmingthat the caller ID has been normally received, the RCIU 12 transfers thecaller ID to the RCTU 16 through the data highway 17; otherwise, theRCIU 12 transfers an error code to the RCTU 16. The RCTU 16 analyzes thecaller ID transferred from the RCIU 12 and extracts information such asthe calling line name and calling line number which are used for thesubsequent call processing.

[0243]FIG. 13 is a timing chart showing the caller ID receptionoperation. As shown in FIG. 91, the caller ID arrives at the intervalbetween the first ring (2 sec) and the second ring of a ringing signal.When the ringing signal arrives, the RCIU 12 detects the end of thefirst ring of the ringing signal and then waits for the arrival of thecaller ID. The RCIU 12 sequentially receives the channel seizure signal,the mark signal, and the actual data, and finally, the checksum. Uponreceiving all of these signals, the RCIU 12 transfers these signals tothe RCTU 16 through the data highway 17.

[0244] When the start of reception of the first ring of the ringingsignal is detected, the RCTU 16 sets a privacy mode for the CO linewhich has received the signal, thereby preventing congestion of callingand call reception. The privacy mode is canceled upon detecting thestart of reception of the second ring of the ringing signal. The callerID is not always constituted by a piece of information (message type)and may have a plurality of pieces of information (a plurality ofmessage types). Therefore, in receiving the caller ID, the RCIU 12confirms the message type and receives all pieces of information.

[0245] The RCTU 16 analyzes the transferred caller ID to determine thecalled telephone and causes the telephone to generate sound. FIG. 14 isa flow chart showing the control procedure.

[0246] In step S14 a, the RCTU 16 analyzes the caller ID to detect thecalling line number. In step S14 b, the RCTU 16 accesses a table memorystoring the correlation between calling line numbers and soundgeneration telephone numbers. In step S14 c, it is determined whetherthe called telephone number corresponding to the received calling linenumber is stored.

[0247]FIG. 15 shows an example of the table memory which is arranged inthe RAM 163 shown in FIG. 8. The storage contents of this table memory,i.e., the correlation between the calling line numbers and the soundgeneration telephone numbers is set in advance upon wiring installation.The user of an extension telephone who has done the answering operationfor the call arriving from the CO line for the first time, including atransfer operation to another extension telephone (RT: Ring Transfer),can operate the extension telephone, as needed to change the soundgeneration telephone number stored in the table memory to the selfextension telephone number. In addition, the sound generation telephonenumber stored in the table memory can be automatically rewritten to thenumber of the extension telephone which has answered the call for thefirst time. Furthermore, in place of or in addition to the calling linenumber, the name of the calling line contained in the caller ID may beregistered in the table memory.

[0248] When it is determined in step S14 c that the called telephonenumber corresponding to the received calling line number or calling linename is stored, the RCTU 16 advances to step S14 d. The telephonecorresponding to the stored telephone number is determined as the calledtelephone, and the RDKU 13 sends call reception information to thistelephone and causes it to generate sound. If no corresponding calledtelephone number is stored, the flow advances to step S14 e to performthe normal call reception operation. In the normal call receptionoperation, a repeater (ATT) or a predetermined extension telephonereceives the call.

[0249] Upon receiving the call reception information, the extensiontelephone displays the calling line name, the number of the CO linewhich has received the call, or the like on the LCD 28, as shown in FIG.16. In normal call reception to the repeater, the calling line name, thenumber of the CO line which has received the call, and the like aredisplayed on the LCD of the repeater, as shown in FIG. 17.

[0250] Assume that the user of the extension telephone which hasreceived the call temporarily answers the call and then transfers it toanother extension telephone, i.e., an RT (Ring Transfer) operation isperformed. In this case, the RCTU 16 causes an extension telephonecorresponding to the extension telephone number as the transferdestination input by the transfer operation to receive the call. In RT,the RCTU 16 sends the caller ID to the extension telephone of thetransfer destination, and the caller ID is displayed on the LCD of theextension telephone of the transfer destination. In recalling RT, thecall is received by the extension telephone of the transfer sourceagain. At this time, the received caller ID is displayed on the LCD ofthe extension telephone which has received the call.

[0251] With the above operation, an optimum extension telephone user cananswer each calling line. For example, a terminal for receiving andanswering a call can be appropriately selected such that a person incharge directly answers a call from an important client while asecretary answers calls from other clients.

[0252] (1-2) Storage of Caller ID

[0253] If nobody answers the call from the CO line, and the calling linequits calling, the received caller ID is stored in a storage bufferallocated to each extension terminal.

[0254] Assume that nobody answers the call from the CO line, and thecalling line quits calling. Upon determining that the office line callreception is restored, the RCTU 16 stores the received caller ID in astorage buffer corresponding to the called extension line in the buffermemory area in the RAM 163. In storing the received caller ID, if thestorage buffer has a free area, the received caller ID is written in thefree area. If no free area is present, the received caller ID isoverwritten on the oldest caller ID. The caller ID to be stored has thecalling line name (15 characters), the calling line number or ID code(10 digits), the call reception date (8 digits), and the status(contents of storage data or data reference condition).

[0255] If RT is performed, and the extension telephone of the transferdestination does not answer the call, the received caller ID is storedin the storage buffer corresponding to the extension line of thetransfer destination. In recalling the call transfer, the receivedcaller ID is stored in both the storage buffer of the transfer sourceextension line and that of the transfer destination extension line.

[0256] Assume that call forward (CF) has been set in the extensiontelephone which has received the call. If a call is received by anotherextension telephone, the extension telephone of the CF destination doesnot answer the call, and calling is quitted, the received caller ID isstored in the storage buffer corresponding to the extension telephone ofthe CF source.

[0257] When only one extension telephone corresponds to the CO linewhich has received the call, the caller ID is stored in the storagebuffer corresponding to this extension telephone. If two or moreextension telephones correspond to the CO line, the caller ID isreceived in the buffer corresponding to a predetermined extensiontelephone corresponding to the call reception CO line.

[0258] If a primary DN or a phantom DN is designated as a called party,the caller ID is stored in the buffer corresponding to an owner terminalcorresponding to the DN.

[0259] By storing caller IDs in correspondence with the respectiveextension telephones, the following effects can be obtained.

[0260] (1-2-1) The user of each extension telephone can refer to thestored caller IDs by a read operation or delete them as needed. That is,the user can generate and manage the list of necessary caller IDs on theself extension telephone. If the list desired by each user is to bemanaged on the main unit, the load on the main unit increases.

[0261] (1-2-2) Call back (to be described later in detail) can beperformed using the stored data.

[0262] (1-2-3) The number of IDs to be stored can be arbitrarilyassigned to each extension telephone. For example, a large storage areacan be assigned to an extension line to be used by a secretary tofrequently receive a call, and a small storage area can be assigned toan extension telephone set in a warehouse to rarely receive a call.Therefore, the limited storage area of the storage buffer can beeffectively utilized.

[0263] (1-2-4) By allowing only a corresponding extension telephone toread the caller IDs stored in the storage buffer or causing eachextension user to use a password, the privacy of the stored caller IDscan be protected.

[0264] (1-3) Display of Stored Caller ID and Call Back

[0265] The stored caller IDs are used to confirm the calling line orperform call back by the user operation.

[0266] Assume that the user of an idling extension telephone operates,e.g., “mode key +62” to display the caller IDs. The extension telephoneshifts to a stored information display mode and sends a caller IDdisplay request to the RCTU 16. To end display, e.g., “mode key +0” isoperated.

[0267] Upon receiving the caller ID display request from the extensiontelephone, the RCTU 16 first reads out, e.g., the latest caller ID fromthe storage buffer corresponding to the extension telephone, transfersthe caller ID to the extension telephone of the request source, andcauses it to display the caller ID on the LCD 28. Every time a scrolloperation is performed on the extension telephone, the RCTU 16 reads outthe caller IDs from the storage buffer one by one from the latestreception timing, transfers the caller ID, and causes the extensiontelephone to display the caller ID on the LCD.

[0268] When a call is received in the caller ID display, mode, theextension telephone blinks the LED and generates sound while keeping thecaller ID displayed. Upon answering the call, the extension telephoneexits the stored information display mode. After this, the displayoperation upon receiving a call is performed on the LCD, as shown inFIG. 16.

[0269] Assume that an operation of accessing the CO line is performed onthe extension telephone in the caller ID display mode. At this time, theRCTU 16 of the main unit 1 executes call back control. FIG. 18 is a flowchart showing the procedure and contents of the control.

[0270] When the DN key or CO key of the extension telephone is depressedduring display of the caller ID, the RCTU 16 detects this operation instep S18 c, and the flow advances to step S18 d. In step S18 d, thecaller ID being displayed is read out from the storage buffer and savedin a dialing buffer. It is determined in step S18 e whether the lineselected by the DN key or CO key is an ACC line which can be used by aspecific person or a general line which can be used by anyone. If theline to be used is an ACC line, the account code input by the user fromthe extension telephone is received in step S18 f and approved in stepS18 g. If the code is approved, the flow advances to step S18 h tocapture the CO line to be used for calling. In this state, when atrigger key (CLID key) for sending an ID is depressed on the extensiontelephone, the flow advances from step S18 i to step S18 j to read outthe caller ID saved from the dialing buffer and send the caller ID tothe captured CO line.

[0271] If the line to be used is a general line, the RCTU 16 omitsapproval of the account code. The flow advances from step S18 e to stepS18 h to capture the line to be used. In this state, when the CLID keyis depressed on the extension telephone, the flow advances from step S18i to step S18 j to read out the caller ID from the dialing buffer andsend it to the CO line.

[0272] If the lowest cost route (LCR) function is set, the RCTU 16performs processing of selecting the lowest cost route before capturingthe line to be used, and a call is sent to the selected route.

[0273] As described above, automatic call back using the stored callerID is allowed. When a call has been received in the absence of anextension telephone user, the user can perform call back only byperforming the call back request operation without performing thedialing operation. Therefore, the user operation associated with thecall back operation can be simplified.

[0274] (1-4) Dump Output of Received Caller ID

[0275] The RCIU 12 has, as modes of transferring the received caller IDto the RCTU 16, a normal mode of analyzing the received caller ID andoutputting the analysis result to the RCTU 16, and a dump mode ofdirectly transferring the received modem data to the RCTU 16 without anyprocessing for the purpose of maintenance/inspection of the RCIU 12itself. The RCIU 12 selects one of the modes in accordance with adownward link transmission code sent from the RCTU 16 through the datahighway 17.

[0276] In the normal mode, the maintenance operator inputs a mode changecommand from the maintenance personal computer to test the operation ofthe RCIU 12. The RCTU 16 transmits a dump mode switching code (00010001)to the RCIU 12 through the data highway 17, as shown in FIG. 19A. Uponreceiving the dump mode switching code, the RCIU 12 changes the selfmode from the normal mode to the dump mode, and then returns a dump modestart code (00010001) to notify the RCTU 16 of the start of a dumpoutput operation from the next received data. After this, every time aringing signal arrives, modem data read from the modem port is directlytransferred to the RCTU 16. The RCIU 12 reads a predetermined amount ofdump data and outputs it to the RCTU 16 while storing the dump data inthe internal buffer. After a predetermined amount of dump data istransmitted to the RCTU 16, the RCIU 12 waits for transmission for apredetermined time in consideration of the time required for the RCTU 16to process the data. After this predetermined time has elapsed, the nextdump data in a predetermined amount is transmitted.

[0277] When the test is complete, and the maintenance operator inputs amode change command, the RCTU 16 transmits a normal mode switching code(00010000) to the RCIU 12 through the data highway 17, as shown in FIG.19. Upon receiving the normal mode switching code, the RCIU 12 changesthe self mode from the dump mode to the normal mode, and then returns anormal mode start code (00010000) to notify the RCTU 16 of the start ofanalyzed data output from the next received data as the normaloperation. After this, every time a ringing signal arrives, caller IDdata read from the modem port is analyzed, and the analysis result istransferred to the RCTU 16.

[0278] As described above, the RCIU 12 reads a predetermined amount ofdump data and transmits it to the RCTU 16 while storing the dump data inthe internal buffer. When the internal buffer is filled, the dump modeis ended at that time point. A dump mode end code (00010010) istransmitted to the RCTU 16 to notify it of the end of the dump mode.

[0279] Although mode switching can be set in units of CO lines, two ormore lines are not simultaneously set in the dump mode. Upon powering on(starting), the normal mode is set for all CO lines. At this time, thenormal mode start code (00010000) is not transmitted from the RCIU 12 tothe RCTU 16.

[0280] As described above, the RCIU 12 has the dump mode and is changedfrom the normal mode to the dump mode, as needed. With this arrangement,in maintenance/inspection, a fault occurrence position can be detectedusing the caller ID arriving from the analog telephone network. As aresult, the fault can be relatively easily and properly disconnected anddetermined, so a measure against the fault can be appropriately andquickly taken.

[0281] (2) Various Operations Associated with Function Setting andMaintenance of System

[0282] (2-1) Prevention of Congestion among A Plurality of Wiringinstallation Terminals

[0283] The basic cabinet la of the main unit 1 has six slots S11 to S16for accommodating main interface units. Of the slots S11 to S16, theslots S11 and S12 receive the RSIU 14 and the RDKU 13, respectively.Wiring installation is normally performed using the digital keytelephone 2 connected to the sixth port of the RDKU 13.

[0284] However, when the user does not use the RSIU 14, the RDKU 13 isalso connected to the slot S11. In this case, wiring installation canalso be performed from the digital telephone connected to the sixth portof this RDKU 13. When two digital telephones can perform wiringinstallation, wiring installation from the two digital telephones maycongest.

[0285] To prevent this, the RCTU 16 of the system of this embodiment hasa wiring installation regulation function.

[0286] More specifically, when wiring installation is to be performed,the maintenance operator inputs a special number, e.g., “*#*#1*2*3”representing a wiring mode start request from the digital telephoneconnected to the sixth port of the slot S11 or S12.

[0287] As shown in FIG. 92, the RCTU 16 determines in step S92 a whetherthe digital telephone which has sent the wiring mode start request is inthe normal mode. If YES in step S92 a, it is determined in step S92 bwhether the wiring flag is OFF. If YES in step S92 b, the flow advancesto step S92 c to turn on the wiring flag ON. In step S92 d, the digitaltelephone which has sent the wiring mode start request is set in thewiring installation mode. After this, the digital telephone can performan input operation for wiring installation.

[0288] When the digital telephone which has sent the wiring mode startrequest is not in the normal mode, or even in the normal mode, thewiring flag is already ON, the wiring mode start request is rejected. Amessage representing the reason for rejection is sent from the RCTU 16to the digital telephone of the request source and displayed on the LCD28.

[0289] Therefore, when the digital telephone connected to one of theslots S11 and S12 is in the wiring mode, the digital telephone connectedto the other slot never changes to the wiring mode even when it sendsthe wiring mode start request.

[0290] With this function, simultaneous function setting inputs from aplurality of wiring installation terminals can be prevented, andcongestion of function setting processing from a plurality of wiringinstallation terminals can be prevented.

[0291] Assume that, upon completing wiring installation, the maintenanceoperator dials a special number, e.g., “##+hold key” representing awiring mode end request from the digital telephone. As shown in FIG. 93,the RCTU 16 determines in step S93 a whether the digital telephone ofthe request source is in the wiring mode. If YES in step S93 a, thewiring flag is turned off in step S93 b. The digital telephone which hassent the wiring mode end request is changed from the wiring mode to thenormal mode.

[0292] (2-2) Error Prevention in Function Setting

[0293] In wiring, telephone numbers are set for the extension ports, orfunctions are assigned to the buttons of the digital telephone. Due tomisunderstanding or erroneous input by the wiring installation operator,one function may be set for a plurality of ports, or a plurality offunctions may be set for one port.

[0294] In the system of this embodiment, the following measure is takento prevent such erroneous function setting. When one function is set foronly one port after power-on, this setting is valid. However, when onefunction is set for a plurality of ports, setting for the port with thesmallest ordinal number is valid, and that for the remaining ports isinvalid.

[0295]FIG. 20 is a flow chart showing the procedure and contents offunction setting determination processing upon powering on. In steps S20a and S20 b in FIG. 20, a port number and a temporary port number areset at “0” as initial values. The temporary port number means an areafor directly saving functional setting contents. The RCTU 16 detects avalid function and port number from this area and uses them.

[0296] In step S20 c, it is determined whether the port number largerthan the temporary port number. If NO in step S20 c, the flow advancesto step S20 f to validate the function set for the port number. In stepS20 g, the port number is incremented by one, and it is determined instep S20 h whether all ports are processed. If unprocessed ports remain,the flow returns to step S20 b to set the temporary port number at “0”again.

[0297] If YES in step S20 c, the flow advances to step S20 d todetermine whether the function set for the port number matches that setfor the temporary port. If YES in step S20 d, it is determined that onefunction is set for a plurality of ports, or this function is alreadyvalid for the temporary port number. In step S20 g, the port number isincremented by one, and the flow advances to determination processing ofthe next port. If NO in step S20 d, the temporary port number isincremented by one in step S20 e. The flow returns to step S20 c torepeat processing from step S20 c.

[0298] Function setting change during the operation of the system willbe described next. In this case, when the function newly set for anarbitrary port does not work at any other ports, the new functionsetting for the port is valid. However, when the newly set functionalready works at another port, the newly set function is regarded astemporary setting, and the function set for another port is made tocontinuously work. In this state, upon powering on again, one functionis set for a plurality of ports, so the function set for the port withthe smallest ordinal number is valid.

[0299]FIG. 21 is a flow chart showing the procedure and contents ofdetermination processing when function setting is performed during theoperation of the system. In step S21 a in FIG. 21, the temporary portnumber is set at “0” as an initial value. In step S21 b, it isdetermined whether the temporary port number matches the port number tobe changed. If NO In step S21 b, it is determined in step S21 c whetherthe function at the temporary port number equals the function to bechanged. If YES in step S21 c, the newly set function works at anotherport. Function determination processing is ended. If NO in step S21 c,the flow advances to step S21 d to increment the temporary port numberby one. If YES in step S21 b, the flow advances to step S21 d toincrement the temporary port number by one.

[0300] When the temporary port number is incremented by one, the flowadvances to step S21 e to determine whether all ports are checked. Ifunchecked ports remain, the flow returns to step S21 b to repeat theabove determination processing. If YES in step S21 e, the newly setfunction works at any other ports. The flow advances to step S21 f tovalidate the function set for the port number to be changed.

[0301] With this function, even when functions with different contentsare set from the personal computer, one of the functions is validated inaccordance with a predetermined rule. For this reason, even when aplurality of inconsistent functions are set, the system can be preventedfrom erroneously operating.

[0302] (2-3) Switching of Connection Interface in RSIU 14

[0303] As shown in FIG. 7, the RSIU 14 has the serial communication port1413 with the RS232C interface function and the modem interfacefunction, which switches these functions by the switching circuit 141 e.The serial communication port 1413 is used in the following forms.

[0304] To use the serial communication interface function, the switchingcircuit 141 e is set to the RS232C driver/receiver 141 b side inaccordance with a switching instruction from the RCTU 16, as shown inFIG. 22. The personal computer 3 as an external information device isconnected to the RSIU 14. For this reason, the user can set the functionof the system or confirm the set information in the system by using thepersonal computer 3.

[0305] To use the modem interface function, the switching circuit 141 eis set to the side of the modem 141 c and the codec 141 d in accordancewith an instruction from the RCTU 16, as shown in FIG. 23. The personalcomputer 3 as an extension terminal device is connected to the RSIU 14through the PCM highway 18 and the RDKU 13. For this reason, the usercan perform function setting by using the personal computer serving asan extension terminal device. This use form can be set by inputting acommand from the personal computer 3 as an extension terminal device tothe RCTU 16.

[0306] Another example of use of the modem interface function is shownin FIG. 24. The main unit 1 is called from the personal computer 3 in aremote site through the analog telephone network NW. After the responseof the main unit 1, a command is input from the personal computer 3 tothe RCTU 16. A switching instruction is sent from the RCTU 16 to theRSIU 14, and accordingly, the switching circuit 141 e in the RSIU 14 isswitched to the side of the modem 141 c and the codec 141 d.Subsequently, the personal computer 3 in the remote site is connected tothe RSIU 14. The user can set the function of the system or confirm theset information in the system by using the personal computer 3.

[0307] As a result, data can be transmitted/received not only to/fromthe personal computer 3 connected to one of the serial communicationports 1410 to 1413 as an external information device but also to/from apersonal computer connected as an extension terminal device or apersonal computer in a remote site, which is connected through theanalog telephone network NW.

[0308] (2-4) Loop Back Transfer in RSIU 14

[0309] The RSIU 14 has a loop back function for the RS232C port. Asshown in FIG. 7, the RSIU 14 has a normal mode wherein data sent fromthe personal computer 3 is received by one of the serial communicationports 1410 to 1413 and then transferred to the RCTU 16 through the CPUbus 143 and the dual port RAM 142, and a loop back mode wherein datasent from the personal computer 3 is received by one of the serialcommunication ports 1410 to 1413, temporarily stored in the RAM 142through the CPU bus 143, and then read out and transmitted from one ofthe serial communication ports 1410 to 1413 to the personal computer 3of the data transmission source. Data transmission control in thesemodes is performed by the control section 140 in accordance with aninstruction from the RCTU 16.

[0310] By using this function, the operation of, e.g., the main unit 1can be evaluated. A personal computer having an evaluation function isconnected to one of the serial communication ports 1410 to 1413.Evaluation data is transmitted from the personal computer while thetransmission mode of the RSIU 14 is set in the normal mode and in theloop back mode.

[0311] In the normal mode, the evaluation data is received by the serialcommunication port, transferred to the RCTU 16 through the CPU bus 143,returned from the RCTU 16 to the RSIU 14 through the CPU bus 143, andthen returned from the serial communication port to the personalcomputer of the evaluation data transmission source.

[0312] To the contrary, in the loop back mode, the evaluation data isreceived by the serial communication port, temporarily stored in the RAM143 through the CPU bus 143, and then read out and returned from theserial communication port to the personal computer of the evaluationdata transmission source.

[0313] The personal computer analyzes the evaluation data returned inboth the modes and compares the data. It is determined on the basis ofthe analysis result whether a fault is present in the RSIU 14 itself oranother unit such as the RCTU 16.

[0314] (2-5) Confirmation of Operation of Arbitrary Unit in Main Unit 1

[0315] The system of this embodiment can individually evaluate theoperation of an arbitrary unit in the main unit 1. A monitor unit isconnected to one of the serial communication ports 1410 to 1413 in theRSIU 14. A unit to be evaluated is individually selected from the unitssuch as the RCOU 11, the RCIU 12, the RDKU 13, the RSTU 15, and thelike. An evaluation unit is connected to the selected unit to supplyevaluation data. The evaluation data is an ASCII code or a command forremote maintenance of the main unit, which is input from a personalcomputer.

[0316] The unit to be evaluated operates in accordance with theevaluation data. Data generated by the operation is transferred to theRCTU 16 through the data highway 17 and then transmitted from the RCTU16 to the monitor unit through the RSIU 14. The monitor unit displays orprints the operation result data transmitted from the main unit 1.Therefore, the inspector or maintenance operator of the product canevaluate the operation state of the unit to be evaluated on the basis ofthe data displayed on or printed by the monitor unit.

[0317] For example, in the normal mode, a command for remote maintenanceis input. If normal response data is returned from the main unit anddisplayed on the monitor unit, it is determined that the unit to beevaluated is normal. However, when abnormal response data is returned,the loop back mode is set, and an arbitrary ASCII code is input from thepersonal computer. If this input ASCII code is returned and displayed onthe display of the personal computer without any change, it isdetermined that the data transmission system between the personalcomputer and the main unit is normal. In this case, it is determinedthat the remote maintenance program of the main unit has a problem. Ifthe input ASCII code is not returned or displayed on the display, it isdetermined that the data transmission system between the personalcomputer and the main unit is abnormal.

[0318] (2-6) Wiring Installation of Transmission Rate for SerialCommunication Ports 1410 to 1413 in RSIU 14

[0319] The total data transmission rate provided by the RSIU 14 is setat, e.g., 9,600 bps. When a transmission rate is permanently assigned tothe serial communication ports 1410 to 1413 within this range of thetotal transmission rate, the transmission rate is 2,400 bps. However,all serial communication ports are not always connected to personalcomputers. In this case, the transmission capability of the RSIU 14 ispartially unused.

[0320] To prevent this, in the system of this embodiment, the RSIU 14has a function of assigning and controlling an adaptive datatransmission rate. The RSIU 14 stores a table storing the correlationbetween the number of ports to be used and the data transmission rate inthe RAM 142. FIG. 25 shows an example of the table storing thecorrelation between the number of ports to be used and the datatransmission rate. In wiring installation, the control section 140assigns a transmission rate to each port. Every time a transmission rateis assigned, it is checked with reference to the table whether the totaltransmission rate does not exceed 9,600 bps. If the total transmissionrate exceeds 9,600 bps, the user is notified of the error. The userchecks transmission rate setting for the remaining ports and reassigns atransmission rate to the target port. If the sum of the assignedtransmission rates is equal to or smaller than 9,600 bps, this wiringinstallation is valid.

[0321] A total of five types of external connection devices can beconnected to the serial communication ports 1410 to 1413: a teletype(TTY), a communication management recording unit (SMDR), a communicationinformation management terminal (MIS), an SMDI, and a CLASS/O.A. Whenthe user determines the type of unit to be connected, i.e., the usepurpose of a port, the communication scheme such as a bit length, i.e.,the transmission attribute is automatically determined by the controlsection 140. FIG. 26 shows the correlation between the use purpose andthe communication scheme.

[0322] In starting for the first time, the first port 1410 is set for aTTY to allow an operation at 2,400 bps while the remaining ports are setin an inoperative state. If wiring installation has been performed uponpowering on, the wiring set value has priority. Therefore, the user canperform wiring installation by using the first port without setting aport to be exclusively used for wiring installation. With thisarrangement, the user can always grasp the transmission rate and is notconfused anymore.

[0323] Presence of the same use purpose at a plurality of ports isinhibited. If a plurality of ports have the same use purpose, the portwith the smallest ordinal number has priority over the remaining ports,and ports with larger ordinal numbers are neglected. This determinationis done by the RCTU 16 when the unit is inserted.

[0324] (2-7) Determination of Capacity (Power Factor) of Units andExtension Terminals in System Installation

[0325] In the conventional power factor determination, the engineermanually calculates the power factor of each unit or digital telephoneto be mounted, and the obtained value is collated with the sum of powerfactors of the system, thereby determining whether the connectioncapacity of the units and digital telephones is appropriate. For thisreason, power factor determination takes much labor and time.

[0326] In the system of this embodiment, the RCTU 16 detects the powerfactor of each of the units mounted in the main unit 1 and the digitaltelephones 2 connected to the RDKU 13 to calculate the sum. Thecalculated value is collated with the rated value of the power factor ofthe system, e.g., 24 V/70 mA. If the resultant value exceeds the ratedvalue, a warning message is sent to the digital telephone or personalcomputer for wiring installation and displayed on the LCD.

[0327] Even when a number of extension terminals beyond the prescribedvalue of the power factor are to be connected by the engineer or thelike, he/she is warned of it by the message. Therefore, mounting andconnection of a number of units and extension terminals beyond theprescribed value of the power factor can be prevented.

[0328] (2-8) Connection between Basic cabinet 1 a and Extension cabinet1 b

[0329] As shown in FIG. 1, the main unit 1 is constituted by stacking aplurality of extension cabinets 1 b on the basic cabinet 1 a andconnecting the basic cabinet 1 a to the extension cabinets 1 b throughdata cables. The data transmission format between the basic cabinet 1 aand each extension cabinet 1 b is individually set on the basic cabinet1 a side in advance in accordance with the stacking position of thebasic cabinet.

[0330] Assume that each extension cabinet 1 b has four slots A, B, C,and D. Let BA, BB, BC, and BD be downward link data transmitted from thebasic cabinet 1 a to the slots A, B, C, and D. The number of channels ofthese downward link data BA, BB, BC, and BD changes for each extensioncabinet 1 b, as shown in FIG. 35. In FIG. 35, EA, EB, EC, and EDrepresent data names in each extension cabinet 1 b.

[0331] For this reason, each extension cabinet 1 b must have a uniquedata transmission function according to its stacking position. In thiscase, however, extension cabinets of different types corresponding tothe number of stages must be prepared, and common extension cabinetscannot be used, resulting in an increase in cost of the system.

[0332] The system of this embodiment solves this problem in thefollowing manner. A cabinet position recognition signal is sent from thebasic cabinet 1 a to each extension cabinet 1 b, and the extensioncabinet 1 b recognizes its stacking position on the basis of the cabinetposition recognition signal. In accordance with the recognized framestacking position, an interframe transmission channel for signaltransmission between the extension cabinet and the basic cabinet 1 a andan intraframe transmission channel for signal transmission between theslots of the self frame are switched, and the number of time slots ofeach channel is converted.

[0333]FIG. 27 is a view showing the connection structure between thebasic cabinet 1 a and the extension cabinets 1 b. FIG. 28 is a blockdiagram showing the arrangement of a connection interface circuit. InFIGS. 27 and 28, only two of a plurality of (five in FIG. 1) extensioncabinets 1 b are illustrated for the descriptive convenience.

[0334] As shown in FIG. 27, a mother board 1 a 1 of the basic cabinet 1a has connectors 1 a 21 and 1 a 22 for connecting extension cabinets.Relay boards 1 b 12 and 1 b 22 of extension cabinets 1 ba and 1 b 2 haverelay boards 1 b 12 and 1 b 22 in addition to various units 1 b 13 and 1b 23 such as the RDKUs 13, respectively. The relay boards 1 b 12 and 1 b22 also have connectors 1 b 16 and 1 b 26, respectively. The connectors1 b 16 and 1 b 26 are connected to the connectors 1 a 21 and 1 a 22 ofthe basic cabinet 1 a through data cables 1 c 1 and 1 c 2, respectively.

[0335] The relay boards 1 b 12 and 1 b 22 have cabinet positionrecognition circuits 1 b 14 and 1 b 24 and channel switching circuits 1b 15 and 1 b 25, respectively. The cabinet position recognition circuits1 b 14 and 1 b 24 recognize the stacking positions of the self frames onthe basis of cabinet position recognition signals sent from the basiccabinet 1 a through the data cables 1 c and 1 c 2 and notify the channelswitching circuits 1 b 15 and 1 b 25 of the recognized cabinet positioninformation. The cabinet position recognition signal is, e.g., a 2-bitsignal generated by selectively connecting two signal lines to the powersupply (5V) and the ground terminal on the mother board 1 a 1 of thebasic cabinet 1 a or generated by the control unit 16.

[0336]FIG. 29 is a table showing the correlation between the extensioncabinets 1 b l and 1 b 2, cabinet position recognition signals AS-1 andAS-2, and a data channel switching signal CS (to be described later).FIG. 30 shows the circuit arrangement of each of the cabinet positionrecognition circuits 1 b 14 and 1 b 24. Each cabinet positionrecognition circuit is constituted by an exclusive OR circuit, aninverter circuit, a pull-up circuit, and a pull-down circuit. Thiscircuit generates inverted cabinet position recognition signals AS-1/and AS-2/ and the data channel switching signal CS in accordance withthe input logic levels of the cabinet position recognition signals AS-1and AS-2.

[0337] Each of the channel switching circuits 1 b 15 and 1 b 25 has adownward link switching circuit for channel-switching downward link datafrom the basic cabinet 1 a to downward link data for a corresponding oneof the extension cabinets 1 b 1 and 1 b 2 and an upward link switchingcircuit for channel-switching upward link data sent from each slot ofthe extension cabinet 1 b 1 or 1 b 2 to upward link data for the basiccabinet la on the basis of the cabinet position recognition signalsAS-1/ and AS-2/ and the data channel switching signal CS output from acorresponding one of the cabinet position recognition circuits 1 b 14and 1 b 24.

[0338]FIG. 32 shows an arrangement of the downward link switchingcircuit. This circuit has a plurality of gate circuits which are turnedon/off in accordance with the cabinet position recognition signals AS-1/and AS-2/. These gate circuits switch the downward link data BA, BB, andBC sent from the basic cabinet 1 a to the downward link data EA, EB, EC,and ED for the slots A, B, C, and D in the extension cabinets 1 b l and1 b 2. FIG. 31 shows the correlation between the basic cabinet side dataBA, BB, and BC and the extension cabinet side data EA, EB, EC, and ED inthe downward link switching circuits of the extension cabinets 1 b 1 and1 b 2.

[0339]FIG. 34 shows an arrangement of the upward link switching circuit.This circuit has three gate circuits which are turned on/off inaccordance with the cabinet position recognition signals AS-1/ and AS-2/and the data channel switching signal CS/, three pull-up circuits forpulling up the output terminals of the gate circuits, and three ANDgates which are turned on in accordance with the output signals from thegate circuits. Upward link data sent from the slots A, B, C, and D inthe extension cabinets 1 b 1 and 1 b 2 are switched to the upward linkdata BA, BB, and BC to the basic cabinet 1 a in accordance with thecabinet position recognition signals AS-1/ and AS-2/ and the datachannel switching signal CS/. FIG. 33 shows the correlation between thebasic cabinet side data BA, BB, and BC and the extension cabinet sidedata EA, EB, EC, and ED in the upward link switching circuits of theextension cabinets 1 b l and 1 b 2.

[0340] With this arrangement, the extension cabinets 1 b 1 and 1 b 2recognize the self stacking positions on the basis of the cabinetposition recognition signals AS-1 and AS-2 from the basic cabinet 1 a.In accordance with the recognition result, the transmission data channelbetween the basic cabinet 1 a and the slots A, B, C, and D in each ofthe extension cabinets 1 b 1 and 1 b 2 is switched. That is, theextension-cabinets 1 b 1 and 1 b 2 autonomously execute channelswitching according to their stacking positions. For this reason, theextension cabinets 1 b 1 and 1 b 2 can have a common arrangement, andthe cost of the extension cabinet can be reduced.

[0341] In the above description, the cabinet position recognitioncircuits 1 b 14 and 1 b 24 and the channel switching circuits 1 b 15 and1 b 25 are mounted on the relay boards 1 b 12 and 1 b 22, respectively.However, these circuits may be directly mounted on mother boards 1 b 11and 1 b 21.

[0342] (3) Characteristic Operation in Sending/Receiving Call and inCommunication

[0343] (3-1) Level Control for DTMF Signal When a dialing signal is tobe sent from the main unit 1 to the public network NW, a DTMF signal isused. At this time, a signaling tone is sent to the calling digital keytelephone 2 in synchronism with the DTMF signal sending operation to thepublic network NW. The signaling tone also uses a DTMF signal. However,the level of the DTMF signal as the signaling tone is set to be lowerthan that of the DTMF signal sent to the public network NW as thedialing signal. For this purpose, conventionally, a tone oscillator forgenerating a DTMF signal as a dialing signal and a tone oscillator forgenerating a DTMF signal as a signaling tone are independently arranged.A dialing signal and a signaling tone each having an appropriate signallevel are sent by biasing the tone oscillators. With this arrangement,however, two tone oscillators having the same arrangement are required,resulting in a complex and expensive unit.

[0344] In the embodiment of the present invention, the time switchsection 165 in the control unit 16 has the digital attenuator section1653, as shown in FIG. 9. The digital attenuator section 1653 has eightattenuators from −18 dB to +3 dB. Every time slot data is input from thedata memory 1652, one of the attenuators is activated in accordance withcontrol data output from the connection memory 1657, so that the inputtime slot data is gain-controlled by the activated attenuator andoutput.

[0345]FIG. 36 shows an example of control data output from theconnection memory 1657. Control data output from the connection memory1657 has eight bits (DO to D7). The signal bits D4 to D6 are used asbits for selecting one of the eight attenuators. The signal bit D3 isused to select one of the μ/L rule and the A/L rule as a coding rule.The μ/L rule is a PCM coding rule mainly used in the North America andJapan. The A/L rule is a PCM coding rule mainly used in England or theSoutheast Asia. By allowing selection of one of the rules, a time switchof certain type can be used in any countries employing different codingrules.

[0346] The signal bit DO is used to control the data output from thedata memory 1652 or the multiplexer 1654 in units of channels. Thesignal bit D2 is used to select one of the switching mode and themessage channel mode.

[0347] With this arrangement, when a dialing signal consisting of a DTMFsignal is to be sent to the public network NW in response to a callingrequest from the digital telephone key DKT, a DTMF signal generated froma tone generator is inserted into two different time slots and input tothe time switch section 165, as shown in FIG. 37A. In the time switchsection 165, an attenuator is selected at the switching timing of thefirst slot of the two time slots to apply an attenuation amount for adialing signal to the DTMF signal. The DTMF signal in the first timeslot is supplied with the attenuation amount for a dialing signal by theattenuator, transferred to the RCOU 11, and sent from the RCOU 11 ontothe CO line toward the public network NW. When the signal sendingdestination is a CO line, an attenuation amount of −15 dB is inserted.

[0348] At the switching timing of the second slot, an attenuator isselected to apply an attenuation amount for a signaling tone. The DTMFsignal in the second time slot is supplied with an attenuation amountfor a signaling tone, i.e., an attenuation amount larger than that forthe dialing signal by the attenuator, transferred to the RDKU 13, andsent from the RDKU 13 to the calling digital key telephone DKT. Theabove attenuation amount is not inserted during speech communicationbetween the extension line and the CO line. An attenuation amount of 8dB is inserted for speech communication between extension lines.

[0349] That is, on the basis of a common DTMF signal generated by onetone generator, a DTMF signal having a signal level suitable for adialing signal and a DTMF signal having a signal level suitable for asignaling tone are generated and sent to the public network NW and thecalling digital key telephone DKT. For this reason, two DTMF generatorshaving different output signal levels need not be prepared, so thecircuit arrangement can be simplified and reduced in size, resulting incost reduction of the main unit.

[0350] The attenuation amount insertion timing by the attenuator islimited to the signal sending timing. For example, in calling the COline, the attenuation amount is inserted only during the dialing inputperiod. After the dialing input period, attenuation amount insertion iscanceled.

[0351] Even when speech communication is performed between the digitalkey telephones DKT through the main unit 1, as shown in FIG. 37B, orspeech communication is performed between office lines through the mainunit 1, as shown in FIG. 37C, the speech communication signal level canbe changed using the signal level changing function of the time switchsection 165. For example, when the received volume from the other partyof speech communication is too small to catch the words, thereception-side speaker performs an operation of increasing the receptionlevel on the self digital key telephone. Control data having a receivedvolume increasing request is sent from the digital key telephone to themain unit 1. In response to the request of the control data, the mainunit 1 changes the attenuation amount of the digital attenuator section1653 in the time switch section 165 to a smaller one at the switchingtiming of the time slot where the reception signal for the digital keytelephone of the request source is inserted. With this operation, thevolume of the reception signal for the digital key telephone of therequest source is increased, and the speaker can obtain a satisfactoryreception quality to catch the words.

[0352] (3-2) Differentiation of Camp-on Tone

[0353] The digital key telephone system according to the presentinvention has a camp-on function. The camp-on function will be describedbelow.

[0354] By employing a multi DN function, various calls are received atDN keys. In this case, if there is an available DN key, a call isreceived at this DN key. However, if all DN keys are used, the call isnot received and waits for an available DN key. At this time, the mainunit send a tone signal to the called DKT and causes it to output atone, thereby notifying the DKT user of call reception. The tone outputfrom the DKT at this time is called a camp-on tone. The camp-on iscalled office line camp-on when a call is received by an office line, orextension camp-on when an extension line receives a call.

[0355] It is very convenient for the user if he/she can determine officeline call reception or extension call reception only by listening to theoutput camp-on tone. The reason for this is as follows. When a new callis received by the office line during extension speech communication,the extension speech communication is immediately ended to answer thecall on the office line because the call is from outside the company. Ifthe call is received by the extension line, the extension speechcommunication can be continued such that the new call is answered afterthe end of the extension speech communication because the call is madeinside the company. As described above, calls can be coped with indifferent manners.

[0356] However, conventionally, only a predetermined type of tone signalis used as the camp-on tone. For this reason, the user cannot determinethe called line, i.e., the office line or the extension line only fromthe camp-on tone.

[0357] According to the present invention, in camp-on, the main unit 1determines extension call reception or office line call reception, andthe camp-on tone to be sent from the main unit 1 to the called DKT 2 inthe busy state is changed in accordance with the determination result.

[0358] For example, for a call from the extension line, an unmodulatedbeep tone having a frequency of 2,000 Hz is sent to the called DKT 2 inthe busy state using an intermittent pattern of 1-sec ON and 3-sec OFF.For a call from the office line, a beep tone having a frequency of 2,000Hz and modulated at 10 Hz is sent to the called DKT 2 using anintermittent pattern of 1-sec ON and 3-sec OFF.

[0359] The arrangement for generating the camp-on tone changes dependingon whether the called terminal is the DKT/EKT 2 or the standardtelephone (STT) 4. The DKT/EKT 2 incorporates a beep tone (2 KHz) soundsource. Therefore, when the called terminal is the DKT/EKT 2, the mainunit 1 sends a command for instructing output of a camp-on tone forextension call reception or a command for instructing output of acamp-on tone for office line call reception to the DKT/EKT.

[0360] To the contrary, the standard telephone 4 has no beep tone soundsource. For this reason, when the called terminal is the standardtelephone 4, the main unit 1 must generate a camp-on tone by itself, mixor insert the camp-on tone into a speech communication signal, and sendit to the standard telephone 4. In the main unit 1 of the presentinvention, the main CPU 161 controls the time switch section 165 in thecontrol unit 16 to connect a sound source channel to the channel for thestandard telephone 4 in a predetermined time.

[0361]FIG. 104 is a flow chart showing the procedure and contents of theabove-described camp-on sending control. Every time a calling requestarrives from the office line (CO line) or the extension line, the RCTU16 of the main unit 1 determines in step S104 a whether the calledterminal is busy. If YES in step S104 a, the flow advances to step S104b to determine whether the called DN is a DN being used. If YES in stepS104 b, the flow advances to step S104 c to determine the call receptiontype.

[0362] If it is determined in step S104 c that a call from the officeline is received, the flow advances to step S104 d to determine whetherthe called terminal is the standard telephone (STT) 4 or the DKT/EKT 2.If the terminal is the DKT/EKT 2, a command for instructing generationof a camp-on tone for office line call reception is sent to the calledDKT/EKT 2 in step S104 e. In the called DKT/EKT 2 in the busy state, theinternal sound source is driven in accordance with the command togenerate a camp-on for office line call reception and notify the user ofthe call reception. As the camp-on tone to be used at this time, a beeptone having a frequency of 2,000 Hz and modulated at 10 Hz is generatedusing an intermittent pattern of 1-sec ON and 3-sec OFF. FIG. 105A showsthe signal waveform.

[0363] When the called terminal is the standard telephone 4, the flowadvances to step S104 f. The RCTU 16 drives a sound source channel fortone generation which is arranged in the main unit 1. The time switchsection 165 is controlled to connect the sound source channel to thereception channel of the called standard telephone 4 intermittently at apredetermined period for office line call reception. Therefore, thecamp-on tone for office line call reception, which is generated by themain unit 1, is mixed or inserted into the reception signal, sent to thestandard telephone 4, and output from the reception loudspeaker togetherwith the reception tone. As the camp-on tone to be output at this time,a beep tone having a frequency of 1,200 Hz and modulated at 4 Hz isgenerated using an intermittent pattern of 1-sec ON and 3-sec OFF. FIG.105B shows the signal waveform.

[0364] If a call is received from the extension line, the flow advancesfrom step S104 c to step S104 g. The RCTU 16 determines whether thecalled terminal is the standard telephone (STT) 4 or the DKT/EKT 2. Ifthe terminal is the DKT/EKT 2, a command for instructing generation of acamp-on tone for extension call reception is sent to the called DKT/EKT2 in step S104 h. In the called DKT/EKT 2 in the busy state, theinternal sound source is driven in accordance with the command to outputa camp-on for extension call reception and notify the user of the callreception. As the camp-on tone to be used at this time, an unmodulatedbeep tone having a frequency of 2,000 Hz is generated using anintermittent pattern of 1-sec ON and 3-sec OFF. FIG. 105C shows thesignal waveform.

[0365] When the called terminal is the standard telephone 4, the flowadvances to step S104 i. The RCTU 16 drives the sound source channel fortone generation which is arranged in the main unit 1. The time switchsection 165 is controlled to connect the sound source channel to thereception channel of the called standard telephone 4 intermittently at apredetermined period for extension call reception. Therefore, thecamp-on tone for extension call reception, which is generated by themain unit 1, is mixed or inserted into the reception signal and sent tothe standard telephone 4. As the camp-on tone to be used at this time,an unmodulated beep tone having a frequency of 1,200 Hz is generatedusing an intermittent pattern of 160-msec ON and 3-sec OFF. FIG. 105Dshows the signal waveform.

[0366] With this arrangement, the DKT user who has received camp-onnotification can identify whether the called line is the extension lineor the office line from the difference between camp-on tones. On thebasis of the identification result, the user can determine whetherhe/she should immediately answer the call or may answer the call afterthe current extension speech communication is complete.

[0367] It is determined whether the called terminal is the DKT/EKT 2 orthe standard telephone 4, and if the terminal is the DKT/EKT 2, acommand is sent from the main unit 1 to cause the DKT/EKT 2 to generateand output the camp-on tone. If the called terminal is the standardtelephone 4, the camp-on tone is generated in the main unit 1 and sentto the standard telephone 4, so that the camp-on tone is output from thestandard telephone 4. For this reason, both the DKT/EKT 2 and thestandard telephone 4 can output the camp-on tone according to thepresent invention.

[0368] (3-3) Display of Directory Number (DN)

[0369] The digital key telephone system according to the presentinvention has a multi DN function. In the multi DN function, a pluralityof directory numbers are set in correspondence with different DN keys ofeach digital key telephone, and various control operations includingcall sending/reception in the office line and extension line, varioustransfer operations such as call forward (CF), conference speechcommunication, voice calling (HFU), message waiting (MW), and call park(CP) are performed using the directory numbers. The directory numbersare classified into a primary DN handled as a representative number, asecondary DN handled as a subordinate number, and a phantom DN handledas a virtual number. These directory numbers are arbitrarily set in onedigital key telephone.

[0370] Operation examples of use of the DNs in the digital key telephoneDKT will be described.

[0371] 3-31 Extension Speech Communication Using DN Keys

[0372]FIG. 95 is a view for explaining this operation. Assume that theuser of the DKT 200 performs an off-hook operation and depresses theDN200 key. An LED corresponding to the DN200 key blinks to display thatthe DN200 is being used. Upon depressing the DN200 key, the DKT 200outputs a dialing tone. When the user who confirmed the dialing tonedials the extension number of the DKT 201, a call signal is sent fromthe main unit to the DKT 201. The called DKT 201 outputs an extensionringing tone, and at the same time, an LED corresponding to the DN201key blinks to indicate that the DKT 201 is being called.

[0373] In this state, the user of the DKT 201 performs the off-hookoperation or depresses the DN201 key, the calling DKT 200 and the calledDKT 201 are connected by the main unit to allow speech communicationbetween the DKTs 200 and 201. In the speech communication state, the LEDcorresponding to the DN201 key of the called DKT 201 blinks to indicatethat the DKT 201 is being used. When speech communication is ended, andone of the DKTs performs a speech communication ending operation, theextension lines are disconnected, and the LEDs of the DKTs 200 and 201are turned off.

[0374] 3-32 Setting of CF Destination DN Using Primary DN Key

[0375]FIG. 96 is a view for explaining this operation. When a CFdestination is to be set using the primary DN key, the user of the DKT200 of the CF setting source depresses the DN200 key, confirms thedialing tone, and then dials a CF setting special number “#601”. Next,the user dials the extension number of the DKT 201 as the CFdestination. Finally, the user depresses the RDL key to end setting.After this, a call received by the DN200 is transferred to the DN201 bythe main unit.

[0376] 3-33 Setting of CF Destination Using Phantom DN Key

[0377]FIG. 97 is a view for explaining this operation. A descriptionwill be made below assuming that the DKT 200 is registered in advance asthe owner terminal of the DN500. To set the CF destination using thephantom DN key, the user of the DKT 200 of the CF setting sourcedepresses the phantom DN500 key. The user confirms the dialing tone,dials the CF setting special number “#601”, and then dials, e.g., theextension line, 203, of the DKT 203 as the CF destination. Finally, theuser depresses the RDL key to end CF setting. After this, a callreceived by the DN500 of the setting source is transferred to the D 203.

[0378] 3-34 Setting of Voice Mail ID Code Using Primary DN Key

[0379]FIG. 98 is a view for explaining this operation. When a voice mailID code is to be set using the primary DN key, the user of the DKT 200as the setting source depresses the DN200 key. The user confirms thedialing tone, dials a special number “#656” for setting the voice mailID code, and dials the ID code. The user finally depresses the RDL keyto end voice mail ID code setting.

[0380] A method of using the voice mail ID code will be described. Theuser performs, on the self DKT 200, an operation of setting the voicemail unit as the CF destination before he/she leaves the position. Afterthis, a call received by the DKT 200 is transferred to the voice mailunit by the main unit so that the message from the calling line isrecorded in the voice mail unit. The voice mail ID code represents anaddress for recording the message. When the voice mail unit answers thecall, the voice mail ID code is sent from the main unit to the voicemail unit as a DTMF signal. With this operation, an address of the voicemail unit is designated to store the message.

[0381] When the message is recorded in the voice mail unit, the DKT ofthe CF source blinks a message lamp to notify the user that the messageis recorded. The message lamp blinks when the voice mail unit sends aspecial number for blinking the message lamp to the DKT.

[0382] In this state, when the user comes back to the position anddepresses the message lamp key, the voice mail unit is called back. Thevoice mail unit answers the call back, reproduces the message from theaddress represented by the ID code, and sends the message to the DKT.

[0383] 3-35 Voice Mail ID Code Setting Using Phantom DN Key

[0384]FIG. 99 is a view for explaining the operation. The user depressesthe phantom DN500 key of the DKT 200 of the setting source. Afterconfirmation of the dialing tone, the user dials #656 or the specialnumber for setting the voice mail ID code and then dials the ID codecorresponding to the phantom DN500. Finally, the RDL key is depressed.With this operation, voice mail ID code setting is complete.

[0385] When a call addressed to the DN500 is transferred to the voicemail unit, the voice mail ID code is sent from the main unit to thevoice mail unit to designate a message storage address.

[0386] 3-36 Display for Confirming DN Number

[0387] In the above-described multi DN function, the user canarbitrarily set a plurality of DN numbers in correspondence with the DNkeys. Therefore, when the user is to use the key telephone of the thirdparty, the user does not know the correspondence between the DN keys andthe DN numbers. Even the user himself/herself may forget the directorynumbers set for the DN keys to hinder call forward setting or the like.In addition, when the installation operator is to test extension callingin installing the system, and the DN numbers of the extension lines areunknown, function setting must be referred to, resulting in aconsiderably cumbersome operation.

[0388] In the system of the present invention, when a directory key ofthe digital key telephone is depressed, and a predetermined specialnumber operation is performed, the main unit 1 reads out the directorynumbers set for the DN keys from the memory and displays them on the LCD28 of the digital key telephone. FIGS. 38A to 38C show examples of theoperation procedure and contents displayed on the LCD 28.

[0389] More specifically, to confirm the directory number set for anarbitrary DN key of the digital key telephone, the object DN key isdepressed first. At this time, “INT” is displayed on the LCD 28 of thetelephone, as shown in FIG. 38A. In this state, when a special number“#401” is input, the directory number corresponding to the DN key,“DN=210”, is displayed on the LCD 28 under the control of the main unit1, as shown in FIG. 38B.

[0390] Directory number confirmation is performed in correspondence witha selected DN key. For this reason, if the special number operation isperformed while the secondary DN key is being selected, the directorynumber of the secondary DN key is displayed. Similarly, if the specialnumber operation is performed while the phantom DN key is beingselected, the directory number of the phantom DN key is displayed.

[0391] When the special number operation is performed to confirm theextension number after the DN key operation, the extension number“INT=210” is displayed, as shown in FIG. 38C. Therefore, the user canconfirm the extension number corresponding to the DN key from thisdisplay.

[0392]FIGS. 39A to 39D show examples of the operation and displayassociated with an inquiry. FIGS. 39A, 39B, 39C, and 39D show DN numberconfirmation, extension number confirmation, accommodation positionnumber confirmation, and slot number confirmation, respectively.

[0393]FIG. 100 is a flow chart showing the procedure and contents of theabove-described DN number display control. When the user depresses a DNkey to be checked, the main unit detects this operation in step S100 a.The flow advances to step S100 b to send a dialing tone to the DKT wherethe DN key is depressed and also send a display control signal to blinkan LED corresponding to the DN key. In step S100 c, a message forpromoting dialing is displayed on the LCD of the DKT. In step S100 d,the DN number of the depressed DN key is read out from the keyarrangement area (RAM) corresponding to the DKT and writes the DN numberin the connection DN area corresponding to the DKT. FIG. 101 shows anexample of this connection DN area.

[0394] If the key depressed on the DKT is a key other than DN keys, theflow advances from step S100 a to step S100 e. The main unit determineswhether the input key is a dial key. If YES in step S100 e, it isdetermined in steps S100 f to S100 i whether the input number is the DNdisplay special number (#407). When it is confirmed that the inputnumber is the DN display special number, the connection DN area issearched for, and the DN number corresponding to the DN key is displayedon the LCD of the DKT.

[0395] In this state, when the user of the DKT performs the on-hookoperation, the flow advances from steps S100 e and S100 k to step S100l. The main unit ends display of the DN number on the LCD of the DKT andrestores calendar display. In step S100 m, the storage contents in theconnection DN area are cleared. In step S100 n, the LED of the DKT isturned off.

[0396] With this function, it can be easily and reliably confirmed thatthe DN key has the primary DN, the secondary DN, or the phantom DN.Therefore, the user and the wiring installation operator can easilydetermine the DN key to be used to set call forward or the like.

[0397] 3-37 Function Setting for Keys of DKT/EKT

[0398]FIG. 102 is a view showing the setting procedure. By dialing thespecial number “*#*#1*2*3” on the DKT as a fixed terminal, the DKT isset in the function setting mode. When a key operation is performed inthe procedure shown in FIG. 102, the function of each key is set. Theset functions are stored in the key arrangement area of the RAM. FIG.103 shows an example of the key arrangement area.

[0399] (3-4) Storage/Display Control of Call Reception Information

[0400] In the digital key telephone system according to the presentinvention, when one or a plurality of calls are received by a busydigital key telephone, pieces of call reception information associatedwith the received calls are stored in the main unit 1. In this state,when a request for knowing the contents of the received calls is sentfrom the busy digital key telephone or a personal computer connected tothe telephone, the pieces of stored call reception information are sentfrom the main unit 1 to the digital key telephone or the calling lineidentification information of the request source and displayed.

[0401]FIGS. 40A and 40B are flow charts showing the procedure of callreception information storage and display control. The main unit 1monitors arrival of a call from the office line in step S40 a. In thisstate, when a call arrives, it is determined in step S40 b whether thecalled digital key telephone 2 is available. If YES in step S40 b, thecall is received by the digital key telephone 2, and call receptioninformation is transmitted to the personal computer 3 and displayed. Instep S40 j, it is determined whether the telephone 2 answers the call.If YES in step S40 j, control is ended without storing the callreception information. If NO in step S40 j, the flow advances to stepS40 d to store the call reception in the call reception answering areain correspondence with the called office line number. This callreception information area is provided in units of digital keytelephones 2.

[0402] If the called digital key telephone 2 is busy, the flow advancesfrom step S40 b to step S40 d to store the call reception in the callreception information area in correspondence with the called office linenumber.

[0403] In this state, assume that the user performs a command inputoperation on the personal computer 3 corresponding to the self digitalkey telephone 2 to know the contents of calls addressed to the user. Thecommand is sent from the personal computer 3 to the main unit 1. Whenthe command is received, the flow advances from step S40 e to step S40f. The main unit 1 checks the corresponding call reception informationarea. In step S40 g, it is determined whether the called office linenumbers in waiting for call reception are stored. If YES in step S40 g,one of the office line numbers is selected in step S40 h to read out thecorresponding call reception information and send it to the personalcomputer of the request source. The call reception information isdisplayed on the display of the personal computer 3.

[0404] If NO in step S40 g, the flow advances to step S40 i to determinewhether all areas are checked. If unchecked areas remain, the flowreturns to step S40 f to check the next area, and call receptioninformation sending and display control is repeated.

[0405] With this operation, pieces of call reception informationaddressed to the user are sequentially displayed on the personalcomputer 3. Therefore, even in the busy state, the user can confirm allpieces of information of calls addressed to the user and waiting forreception on the personal computer 3. An important call can be selectedfrom the calls waiting for reception after the end of speechcommunication, so the user can answer the call.

[0406] In the above description, when a plurality of pieces of callreception information are stored in the call reception information area,the call reception information area is checked by every scroll operationon the personal computer 3. The pieces of call reception information areread out one by one, sent to the personal computer 3 of the requestsource, and displayed on the display of the personal computer 3.However, the present invention is not limited to this. For example, theplurality of pieces of call reception information may be read out atonce in accordance with the request from the personal computer 3, sentto the personal computer 3, and listed on the display of the personalcomputer 3.

[0407] In addition, in the above description, when the user performs acall reception information display request operation on the personalcomputer 3, the call reception information area is checked to send thecall reception information to the personal computer 3 and display it.The display request command may be sent from the personal computer 3 inthe busy state once automatically or periodically, and the main unit 1may check the call reception information area accordingly to send thestored call reception information to the personal computer 3 and displayit. Alternatively, even time a new call arrives in the busy state, themain unit 1 may send the call reception information to the personalcomputer 3 to display it.

[0408] (3-5) Control Associated with Call Park

[0409] In call park, when an extension terminal answers an incoming calland performs a predetermined operation of requesting call park, the callis held at a virtual holding position called a park zone. In this state,when a special number operation of answering the call is performed byanother extension terminal, the extension terminal can reanswer thecall.

[0410] Assume that an extension terminal a answers a call to be receivedby an extension terminal g. When the user of the extension terminal aperforms a special number operation, the call is parked in the parkzone. In this state, the user of the extension terminal a calls theextension terminal g by broadcasting and requests the user of theextension terminal g to answer the parked call. When the user of theextension terminal g performs a predetermined park answering operationin accordance with the request, the extension terminal g and the heldcall are connected to allow the user of the extension terminal g toanswer the call.

[0411] The call is parked in the park zone in correspondence withinformation representing a park address called an orbit number.Conventionally, different orbit numbers are used to park a call for thefirst time and repark the same call. For this reason, when the calledparty does not answer the parked call, and the call is reparked, thesame call is undesirably parked in correspondence with different orbitnumbers.

[0412] To prevent this, in the digital key telephone system of thepresent invention, when a call to be subjected to call park is parked incorrespondence with an orbit number, the orbit number is held until theend of the speech communication of the call. When a call park requestfor the call is generated again during speech communication of the call,the call is parked in correspondence with the held orbit number.

[0413]FIG. 41 shows an example of a park reservation table used for callpark, which is arranged in the memory in the RCTU 16. This parkreservation table has n park areas with orbit numbers #1 to #n. Thenumbers of office line trunks which have received calls to be parked andthe number of terminals which have sent call park requests are stored inthese park areas.

[0414]FIG. 42 is a flow chart showing the procedure of call park controlby the RCTU 16. In step S42 a, the RCTU 16 monitors whether the park keyof the called extension terminal is depressed during office line callreception. In this state, when the park key of the extension terminal isdepressed, the RCTU 16 determines in step S42 b whether the parkreservation table has an available park area, i.e., an available orbit.If YES in step S42 b, the flow advances to step S42 c to perform thepark operation.

[0415] In step S42 d, the number of the trunk which has received thecall and the number of the extension terminal which has sent the parkrequest are stored in one of available orbits. Assume that extensionterminal “005” has sent a park request for a call received by officeline trunk “001”, and orbit #1 is available. In this case, as shown inFIG. 41, the trunk number “001” and the extension terminal number “005”are stored in orbit #1. The RCTU 16 stores orbit number #1 as areservation orbit corresponding to the call until the speechcommunication of the call is ended.

[0416] If NO in step S42 b, park is disabled in step S42 e.

[0417] Assume that the called party does not answer the parked call, andthe user of the extension terminal depressed the call park key again tocall another extension terminal. The RCTU 16 executes park controlagain. FIG. 43 is a flow chart showing the control procedure. When thecall park operation is detected, the flow advances from step S43 a tostep S43 b, and the RCTU 16 determines whether the reservation orbit ispresent. If YES in step S43 b, the flow advances to step S43 c to storethe number of the trunk which has received the parked call and thenumber of the extension terminal which has sent the call park requestagain in correspondence with the reservation orbit.

[0418] If the call park request is sent, and no reservation orbit isstored, the flow advances to step S43 d to disable park.

[0419] Assume that the called party answers the call in park or repark.In this case, the RCTU 16 executes pickup control in the followingmanner. FIG. 44 is a flow chart showing the control procedure. When apickup operation for the parked call is detected, the flow advances fromstep S44 a to step S44 b. The RCTU 16 accesses the reservation orbit ofthe park reservation table to determine whether the call is parked. IfYES in step S44 b, the flow advances to step S44 d to perform pickupcontrol. More specifically, the extension terminal which has answered isconnected to the trunk which has received the parked call to allowspeech communication. If NO in step S44 b, information stored in thecorresponding orbit of the park reservation table is deleted.

[0420] In the system with the above arrangement, when the reparkoperation is performed, the call to be subjected to call park is parkedin correspondence with the same orbit number as that in the precedingcall park. For this reason, the call is prevented from being parked incorrespondence with different orbit numbers.

[0421] (3-6) Control for Mode Change Request from

[0422] Personal Computer In the system according to the presentinvention, an operation mode change request sent from the personalcomputer 3 is transferred to the main unit 1 through the personalcomputer interface unit (PCI-DI) 2 b of the DKT/EKT 2. When the modechange request is transferred, the main unit 1 determines whether themode change request is appropriate and notifies the PCI-DI 2 b of themode change request transfer source of the determination result. ThePCI-DI 2 b performs mode change processing according to the mode changerequest of the personal computer on the basis of the notifieddetermination result.

[0423]FIG. 45 is a flow chart showing the procedure and contents of modechange control in the PCI-DI 2 b and the RCTU 16 of the main unit 1.

[0424] When a mode change command is input from the personal computer 3,the flow advances from step S45 a to step S45 b. The PCI-DI 2 btransfers the mode change command to the main unit 1. The RCTU 16 of themain unit 1 monitors arrival of the mode change command from the PCI-DI2 b in step S45 g. When the mode change command arrives, the flowadvances to step S45 h to analyze the contents of the mode changecommand. In step S45 i, it is determined whether the mode changerequested by the mode change command is allowed. If YES in step S45 i,the mode change command is returned in step S45 j. If NO in step S45 i,the flow advances to step S45 k to return a mode change rejectioncommand to the PCI-DI 2 b.

[0425] After sending the mode change command, the PCI-DI 2 b monitorsreturn of the mode change command and the mode change rejection commandfrom the main unit 1 in steps S45 c and S45 e. In this state, when themode change command is returned from the main unit 1, the flow advancesto step S45 d to execute mode change processing. This mode changeprocessing is performed by the data communication control microcomputer245.

[0426] The PCI-DI 2 b supplies a mode change enable signal to thepersonal computer 3 and at the same time sets the PCI-DI 2 b itself inan operation state corresponding to the changed mode, i.e., a statewherein the extension line is connected to the personal computer. On theother hand, when the mode change rejection command is returned from themain unit 1, the flow advances to step S45 f, and the PCI-DI 2 bexecutes mode change inhibition processing. More specifically, thePCI-DI 2 b notifies the personal computer 3 of mode change inhibition,and simultaneously, sets the self operation state such that even when anoperation corresponding to the changed mode is performed by the personalcomputer 3, the signal is not transferred to the main unit 1.

[0427] As described above, in this system, when the mode change requestis issued from the personal computer 3, the RCTU 16 of the main unit 1always determines whether the request is appropriate. Only when it isdetermined that the request is appropriate, the PCI-DI 2 b is allowed tochange the mode. Therefore, a mode which is not prepared for the mainunit 1 can be prevented from being set in the PCI-DI 2 b.

[0428] For example, assume that the user sends a request for changingthe mode to a computer telephoni mode for calling using the personalcomputer 3. However, when the main unit 1 does not have the computertelephoni mode, the main unit 1 does not return mode change enablenotification. For this reason, the computer telephoni mode is not set inthe PCI-DI 2 b.

[0429] (3-7) Display Control for Held Line

[0430] When a certain digital key telephone 2 holds an office line or anextension line, the number of the held office line or extension line isdisplayed on the LCD 28 of the digital key telephone 2. However, if aplurality of office lines or extension lines are held, the user cannotdetermine the correspondence between the office lines or extension lineswhich are displayed in holding and the flexible buttons.

[0431] In the digital key telephone system according to the presentinvention, when a plurality of office lines or extension lines are held,and a holding information display operation is performed on the digitalkey telephone, the numbers of the plurality of held office lines orextension lines are selectively displayed on the LCD of the digital keytelephone in accordance with the display operation. In addition, theLEDs of the flexible buttons corresponding to the held office lines orextension lines are, e.g., blinked synchronized with the LCD displayoperation.

[0432]FIG. 46 is a flow chart showing the holding display controlprocedure. In the following description, assume that office linescorrespond to 10 flexible buttons 24, and these flexible buttons areused as line selection keys.

[0433] In step S46 a, the RCTU 16 of the main unit 1 monitors whether ascroll key 29 of each digital key telephone 2 in the standby state isdepressed. When the scroll key 29 of an arbitrary digital key telephone2 is depressed, the count value is set at 1 in step S46 b. The flowadvances to step S46 c to search the holding information area for anarea corresponding to the count value=1. The holding information area isarranged in the memory of the RCTU 16 in correspondence with eachdigital key telephone. As shown in FIG. 47, the holding information areastores the held office line numbers in correspondence with the lineselection keys.

[0434] In step S46 d, the RCTU 16 determines on the basis of the searchresult obtained in step S46 c whether the held line number is stored incorrespondence with the first line selection key number. If the heldline number is not stored as in FIG. 47, the flow advances to step S46 gwithout performing held line number display control. The count value isincremented by one. In step S46 h, it is determined whether holdingdisplay control is performed for all of the 10 line selection keys. Inthis case, since line selection keys which have not undergone displaycontrol remain, the flow returns to step S46 c to search for holdinginformation area corresponding to the second line selection key number.It is determined in step S46 d whether the held line number is stored incorrespondence with the second line selection key number. If the heldline number is stored as shown in FIG. 47, the held line number is readout, transferred to the digital key telephone 2, and displayed on theLCD 28 in step S46 e. Simultaneously, an LED control signal is sent tothe digital key telephone 2 to blink the LED 25 corresponding to thefirst line selection key where the held line number is stored. Theblinking frequency is set at, e.g., 10 Hz as a natural frequency toallow discrimination from another blinking display.

[0435] When the held line number is displayed on the LCD 28, and the LED25 is turned on, the flow advances to step S46 g. The RCTU 16 incrementsthe count value by one. In step S46 h, it is determined whether displayand ON-control are performed for all of the 10 line selection keys. IfNO in step S46 h, the flow returns to step S46 c to repeat the abovecontrol.

[0436] As described above, in this system, when the held line numberdisplay operation is performed, the held line number is displayed on theLCD 28, and the LED 25 of the line selection key corresponding to theheld line blinks. Therefore, even when a plurality of lines are held,the user can clearly know the correlation between the held line numberswhich are being displayed on the LCD 28 and the line selection keys.

[0437]FIG. 48 shows an order of blinking the LEDs 25 corresponding toline selection keys 24.

[0438] In the above description, the RCTU 16 of the main unit 1 performsholding display control. However, the microcomputer of each digital keytelephone 2 may perform the control. In the above description, the LEDs25 corresponding to the line selection keys are blinked. However, lineselection key numbers may be displayed on the LCD 28 together with thecorresponding held line numbers. In addition, holding information to bedisplayed on the LCD 28 is not limited to the held line number. A callerID, a directory number, or a user name may be displayed. Furthermore,holding display control for each line selection key may be performed bysequentially selecting a line selection key every time the scroll key 29is depressed.

[0439] (4) Multi DN Function

[0440] In the multi DN function, as described above, a plurality ofdirectory numbers are set in correspondence with different flexiblebuttons in each digital key telephone (DKT), and various controloperations such as call sending/reception from/to the office line orextension line, various transfer operations such as call forward,conference speech communication, message waiting, or call park areperformed using the buttons as DN keys.

[0441] (4-1) Arrangement of DN Keys

[0442] As a DN key arrangement, a single DN key is set for a pluralityof DKTs, or a plurality of identical DN keys are set on one DKT.Alternatively, a phantom DN key is set in addition to the primary DN keyand secondary DN key. FIG. 49 shows an example of the DN keyarrangement, in which “501”, “500”, “200”, “201”, and “202” arearbitrarily set for DKT #200, DKT #201, and DKT #202.

[0443] (4-2) General Description of Various Operations Using DNs

[0444] Operations using the DN keys will be briefly described below.FIGS. 50 to 56 are views for explaining the operations. Symbols in FIGS.50 to 56 represent LED display patterns corresponding to the DN keys andhave meanings defined in FIG. 94.

[0445]FIGS. 50 and 51 show an operation in which voice-calling (HFU) ortone calling is performed, and the called side answers the call, anoperation in which calling by CONF is performed, and the called sideanswers the call, an operation of performing conference by reCONF, andan extension transfer operation.

[0446]FIG. 52 shows an extension ring transfer (extension line R.T)operation, including an operation of R.T call back to the transfer sideat the R.T timeout.

[0447]FIG. 53 shows an ACB (Automatic Call Back) operation. In thisoperation, DKT #200 sets ACB during speech communication of DKT #202,ACB is performed after speech communication of DKT #202, and DKTs #200and #202 answer the call to allow speech communication between the DKTs.

[0448]FIG. 54 shows office line calling and ring transfer operationusing a DN. FIGS. 55 and 56 show an office line calling and conferenceoperation using a DN.

[0449] (4-3) Extension Calling Using DN Keys

[0450] Like the conventional use of INT keys, extension calling can beperformed by an available DN key operation. This also applies to use ofthe primary DN, the secondary DN, or the phantom DN.

[0451] In on-hook calling or SPKR (Speaker Key) calling in the availablestate, when the automatic calling selection function is set to allowextension calling, and there is a DN key which can send a call, DNcalling can be performed by selecting the primary DNs in ascending orderof numbers. If all DNs are not available, calling cannot be performed.For an SLT (Single Line Telephone), when the secondary DN is set for theDKT, the SLT cannot perform calling, though the DN of the SLT can be setfor other extension lines.

[0452] To send a call by depressing another DN key during speechcommunication, the speech communication is ended, and an available DNkey is depressed to allow extension calling. Even when a DN key which isbeing used for speech communication is depressed during the speechcommunication, the speech communication is ended independently ofwhether it is office line or extension speech communication, and newextension speech communication is performed.

[0453] (4-4) Extension Operation

[0454] 4-4-1. In independent extension calling, HFU (Hands Free Unit)calling is used to call only one called DKT of the primary DNs. When aphantom DN is called by HFU calling, the owner terminal is called. Intone calling, only the primary DN or also the secondary DN are calleddepending on setting. Delay call reception is also enabled by setting.HFU calling or OCA calling to the phantom DN cannot be performed. Otheroperations are the same as those for the secondary DN.

[0455] 4-4-2.Independent calling in one voice direction is processed asin HFU calling.

[0456] 4-4-3. In tone calling, even when calling is set, and if callingcannot be performed because of the busy state of the terminal, BOV (BusyOverride) is displayed on the LED of the DN upon call reception, asneeded.

[0457] 4-4-4. LED Display of Extension Call Reception

[0458] In LED display of extension call reception, when a plurality ofcalls are received by longitudinal multiple DNs, “I-Called” is displayedat the key of primary call reception to specify the DN which outputs theringing tone. FIG. 57 shows an example of LED display of DN keys.

[0459] 4-4-5. Even when all DKTs from which the ringing tone is to begenerated are not available, and no ringing tone can be generated, aring-back tone (RBT) is returned to the calling terminal as far as a DNis available. However, when all terminals from which the ringing tone isto be generated are in the DND (DoN't Disturb) state, the RBT isreturned to the calling terminal.

[0460] 4-4-6. No Available DN or No DN Key

[0461] When all primary DN keys set on a certain terminal are notavailable, all of the DNs are not available. For example, when threeprimary DN keys are set on a certain terminal, and all of the threeprimary DN keys are not available, no DN is available. When the DNnumber called is not available, and extension calling is generated, thiscall temporarily becomes busy. A camp-on tone is sent by the operationof the calling line to want for an available DN key. Even when theprimary DKT is available, the busy state is set. Even when the DKTcalled by HFU calling has no primary DN keys, the busy state is set.This is a problem to determine how to perform LED display upon answeringor how to allow a third party to answer when the call is answered andheld.

[0462]FIG. 58 is a table showing an operation when no DN is available orno DN key is available. The camp-on tone when no DN is available is sentto a terminal which is using the called DN and has tone calling callreception setting independently of whether calling is performed as voicecalling or tone calling.

[0463] 4-4-7. Processing of Extension Call Reception During ExtensionCall Reception

[0464] A call arriving during extension call reception is received onlywhen a DN is available. The first call reception has a priority, and thesecond call reception is subjected only to LED display, and no ringingtone is output. HFU calling during extension calling is temporarily setin the busy state and then processed as tone calling by the subsequentoperation. When the second call is a call by HFU calling, and the firstcall reception is stopped, the call is restored as tone calling. This isbecause the calling line is prevented from being confused when the RBTabruptly changes to voice calling. FIG. 59 is a table showing the aboveprocessing of extension call reception during extension call reception.

[0465] 4-4-8. Group calling and broadcasting are performed by functionsetting corresponding to ports. At this time, LED display of the DN keyis not performed on the called side.

[0466] 4-4-9. Switching from tone calling to voice calling is neglectedwhen the DKT having the primary DN is busy or absent. When voice callingis switched to tone calling, a delay ring operation is performed.

[0467] 4-4-10. Busy Override and OCA (Off-hook Call Announce)

[0468] When the called terminal is performing handset speechcommunication, and HFU calling is generated, a BT (Busy Tone) state isset independently of the presence/absence of an available DN. However,if OCA has been set, the terminal is set in the OCA state by theoperation of the calling line. In the system of the present invention,the OCA call reception is not displayed on the LED of the DN key. OCAcontinues even when the connected line is released (held ordisconnected).

[0469] The OCA state can be directly set without intervening the BTstate by wiring installation of automatic OCA.

[0470] Assume that a DN is available. In this state, when tone callingis generated, and a connected line is present, the terminal isautomatically set in the BOV state. When the connected line is released(held or disconnected), the BOV stops, and tone calling is restored. InHFU calling, even when the called terminal is busy, the BOV state is setas far as the called terminal has wiring installation of HFU callingautomatic BOV. When the called terminal is in the DND state, and HFUcalling is busy, processing according to the DND override wiringinstallation of the calling line is performed.

[0471] 4-4-11. When a call reception calling set DKT returns from thenonavailable state to the available state, OCA calling is continuedalthough BOV is switched to tone calling. That is, the call is restored.

[0472] b 4-4-12. ACB

[0473] ACB can be performed by an operation when no DN is available orafter a busy terminal returns a busy tone. ACB occurs when both the DNcalled by ACB and the called DN are available, and both the calling andcalled terminals are available.

[0474] 4-4-13. DND

[0475] The relationship between extension call reception by voice ortone calling and DND is changed by the multi DN function. Tone callingor office line call reception is not performed in the DND state. Voicecalling to a terminal in the DND state is temporarily set in the SBT(Special Busy Tone) state and then in the BOV calling or OCA state bythe operation of the calling line. FIG. 60 shows an example of DNDprocessing during call reception.

[0476] When a DN key as a secondary key does not answer a call of tonecalling, i.e., lateral single appearance occurs, and the called terminalis in the DND state, the SBT is output. When a DN as a secondary DNanswers the call, i.e., lateral multi appearance occurs, the SBT isreturned to the calling line even when all terminals are set in the DNDstate. Once tone calling is performed, the calling line is not set inthe BT state even when all called terminals are in the DND state. DNDoverride by the user operation after the calling line listens to the SBTis performed according to the wiring installation of the calling line.At this time, BOV call reception is performed by all the DND terminals.A terminal which has canceled DND is called by tone calling. DID(Direct-Inward Dialing) or leased line call reception is also set in theDND busy state, like tone calling. However, not the SBT but the BT isoutput, and the call is blocked.

[0477] 4-4-14. Call Forward (CF)

[0478] Call forward is performed in accordance with CF setting at theprimary DN. CF-BUSY is determined when no terminal or DN is availablefor HFU calling and all DNs are not available for tone calling. When noanswer is obtained as a result, call forward is performed. CF can alsobe set for the phantom DN. In this case, a call addressed to the phantomDN is subjected to call forward. FIG. 61 shows the call forwardoperation.

[0479] Even when the phantom DN is set as the CF destination, voicecalling can be performed, like the primary DN. FIG. 62 is a view showingthe operation.

[0480] CF Setting

[0481] CF setting for the primary DN and CF setting for the phantom DNare performed in the following manner.

[0482] “[P DN]+#601, 2, 3, 4, +CF destination [+NA timer]#”

[0483] “[PH DN]+#601, 2, 3, 4, +CF destination [+NA timer]#”

[0484] CF setting for the phantom DN can be performed only from theowner of the phantom DN.

[0485] The CF destination for the primary DN can also be set for thephantom DN. Setting from the phantom DN to the primary DN or anotherphantom DN can also be performed.

[0486] Confirmation of CF Setting by LCD

[0487] A terminal as the owner of the phantom DN can set a plurality ofCF destinations. In this case, to confirm CF setting, the LCD display ofCF destinations is scrolled using the scroll key. FIG. 63 shows adisplay example.

[0488] FCF (Fixed CF)

[0489] In FCF, a call addressed to the primary DN is subjected to CF.

[0490] CF Key (LED)

[0491] The LED of the CF key indicates the CF state of the primary DNand does not display setting for the phantom DN.

[0492] 4-4-15. Station Hunting (SH)

[0493] The SH busy is determined when no terminal or DN is available forHFU calling and all DNs are not available for tone calling. Not only SHfrom the primary DN to the phantom DN but also SH from the primary DN tothe phantom DN and vice versa, or from the phantom DN to another phantomDN can also be performed.

[0494] 4-4-16. Message Waiting (MW)

[0495] MW is received by a called primary terminal. MW to a phantom DNis received by the owner of the phantom DN. At this time, the MW isdisplayed on the phantom MW key. If there is no MW key, the MW cannot bereceived.

[0496]FIG. 64 shows the correlation between phantom DNs and MW keys. Asshown in FIG. 64, the correlation between each phantom DN and a phantommessage waiting key (ph-MW key) is determined in advance. Four MWs canbe set for each phantom DN. Only the owner terminal can have the ph-MWkeys. The ph-MW key is used for display of MW reception and call back.To set MW, the MW key is used.

[0497] LCD Display of MW

[0498] In MW reception, the DN number and terminal number which havereceived the MW are simultaneously displayed on the LCD 28 by operatingthe scroll key 29. FIG. 65 shows a display example. In FIG. 65, “XXXX”represents a DN number which has received the MW, and “YYYY” representsthe telephone number of a terminal for which MW is set.

[0499] In ME transmission, the DN number for which MW is set issequentially displayed by operating the scroll key 29, as shown in FIG.66. In FIG. 66, “xxxx”, “YYYY”, and “ZZZZ” represent DN numbers forwhich MW is set.

[0500] NW Call Back Operation by MW Key

[0501] By depressing a blinking MW key, the primary DN can be captured,and the terminal for which MW is set can be called back. The ph-MW keyis used to capture the phantom DN to send a call. The MW can also be setusing the secondary DN. In this case as well, the primary DN of theterminal for which MW is set is called back. In MW reception by thephantom DN as well, the primary DN of the terminal for which MW is setis called by depressing the ph-MW key.

[0502] MW Reception Operation

[0503] MW reception by the primary DN is performed as shown in FIG. 67.MW reception by the phantom DN is performed as shown in FIG. 68 or 69.

[0504] MW Transmission Operation

[0505] MW transmission from the primary DN is performed as shown in FIG.70. MW transmission from the secondary DN is performed as shown in FIG.71. MW transmission from the phantom DN is performed as shown in FIG.72.

[0506] 4-4-17. DSS (Direct Station Selection) and BLF (Busy Lamp Field)

[0507] A DSS call is used to call not a terminal but a DN. When the DSSkey of an idling terminal is depressed, the primary DN is captured tocall the DN of the other party. BLF display of ATT, DSS, ADM, and LCDindicates not the DN state but the terminal state. Therefore, in theBLF, a DSS call may be set in the BT state when no DN is available butthe terminal is available.

[0508] 4-4-18. Answer to Extension Call Reception

[0509] An extension call reception displayed on the DN key can beanswered by depressing the DN key. Even when another DN key of the sameDN number is depressed, the call cannot be answered. In off-hook or SPKRoperation in the automatic call reception selection mode as well, thecall is answered by the DN with call reception display.

[0510] 4-4-19. Pickup Answering

[0511] Pickup answering can be performed by depressing a DN key withcall reception display. LED display at this time is similar to that ofthe pickup special number. Pickup using the pickup special number canalso be performed by waiting for a dialing tone from another DN key. Todesignate a called extension number, not the DN but the called terminalis designated.

[0512] 4-4-20. Privacy During Extension Speech Communication

[0513] Only one terminal is connected to a DN of one type (e.g.,DN200-1). Privacy cancel or privacy override by the DN is not permitted.

[0514] 4-4-21. ID Sending to Voice Mail

[0515] When the CF destination is a voice mail or MW from a voice mailis called back, and ID sending has been set, an ID is sent. Not only theID of the primary DN but also that of the phantom DN is sent. At thistime, the IDs of the primary DN and the phantom DN are discriminated. IDsetting for the phantom DN is performed by the owner DKT of the DN.FIGS. 73 and 74 are views showing operations of sending the ID to avoice mail for MW and CF, respectively.

[0516] 4-4-22. LCD Messaging

[0517] In tone calling, extension call reception display is performed on(one or a plurality of) terminals capable of receiving a call. When thecalling line is calling from a phantom DN, the terminal number isdisplayed as the calling line number. This also applies to a secondaryDN. When a person other than the called party answers voice or tonecalling, display similar to that in pickup is performed.

[0518] To start character communication, the busy called party depressed“MODE key+2” when the calling line sends an extension call. In the multiDN, character communication is performed when no DNs are available, theother party is busy or receiving a call in HFU calling, and the call byHFU calling is rejected due to DND.

[0519] The LCD can display character communication by the phantom DN, asilent message, or a message for absence answering. For a phantom DN, nounique message is used, and the message of the owner terminal is shared.

[0520] 4-4-23. Buzz (Buzz Tone) Key

[0521] When a Buzz key on a terminal is depressed, a terminal as adestination of the contents of the abbreviated dial corresponding to theBuzz key is called by the Buzz tone and LED. Up to four Buzz keys can beset for one terminal. For example, the Buzz key is used by, e.g., a pairof a boss and a secretary.

[0522] By blinking the LED for 0.5 sec, the reception of the operationis notified to the Buzz key operator. On the called terminal, a Buzztone is generated, and the LED is turned on for 4 sec to notify thereception. When a plurality of Buzz keys are set on one terminal, theBuzz key operator cannot be determined from the tone. However, thecalled party checks the LED to identify the Buzz key operator. FIG. 75shows the operation. FIG. 76 shows the ON timing of the LED of the Buzzkey operation terminal, the ON timing of the LED of the Buzz calledterminal, and the MSG tone generation pattern.

[0523] When the Buzz called terminal is available, the MSG tone isgenerated in a pattern of 1-sec ON, 0.5-sec OFF, and 1-sec ON. When thecalled terminal is not available, a beep tone (10 Hz) is generated in apattern of 1-sec ON, 0.5-sec OFF, and 1-sec ON. The Buzz tone overridesDND and is not influenced even when no DN is available.

[0524] 4-4-24. Camp-on Tone Sending to Single Line Telephone

[0525] When a call arrives at a busy SLT, the call is subjected tocamp-on. In the SLT, the camp-on tone is sent as 2 Beep (not a Beep tonein fact) from the handset. Therefore, the speech communicationinstantaneously stops during the camp-on tone sending period, though itis a minimum time and does not influence on the speech communication.The camp-on tone can be changed between extension call reception andoffice line call reception. For example, as an extension call receptioncamp-on tone (including leased line ring transfer and extension ringtransfer), a message recording box tone (1,209 Hz) intermittently outputin a repeated pattern of 1-sec ON, 3-sec OFF, and 1-sec ON is used. Asan office line call reception camp-on tone (including DID and officeline ring transfer), a message BOX tone (1,209 Hz) modulated at 10 Hzintermittently output in a repeated pattern of 1-sec ON, 3-sec OFf, and1-sec ON is used.

[0526] (4-5) Extension Transfer

[0527] 4-5-1. Extension Ring Transfer

[0528] This system allows extension ring transfer. However, when theterminal which has performed ring transfer (RT) ends speechcommunication after “CONF (Conference) +dial”, the calling DN becomesavailable. Call back to RT is addressed to the DN which has performedRT. In ring transfer, when the DNs of the other party are not available,camp-on is performed. The camp-on tone is sent to a terminal which isusing the called DN and having extension call reception setting.Extension RT call reception to a busy terminal is BOV call reception.LED display of the multi DNs is “I-Called”. Ring transfer is alsodelay-received. Details of the operation are the same as in office linering transfer.

[0529] 4-5-2. Privacy cancel or privacy override by the DN key is notperformed in extension speech communication/conference.

[0530] 4-5-3. In extension calling busy, when dial key 3 is depressed,privacy override is performed. For a DKT having the called primary DN,privacy override is performed for the like used by the terminal.

[0531] (4-6) Office Line Calling

[0532] 4-6-1. An operation of “DN key+dial key 9” allows office linecalling. As a result, the office line can be accessed. When the DKT hasthe office line key, the DN is made available, and display is shifted tothe office line key.

[0533] 4-6-2. Assume that office line calling is to be performed in theautomatic calling selection mode. In this case, when the office line keyof the called office line is not provided, and an access withoutintervening the DN key is performed, it is displayed on the primary DNkey. If the primary DN is not available, calling is disabled.

[0534] 4-6-3. Dial Operation on DN Key

[0535] Redialing, save dialing, trunk queuing, and ABR can be performed.Calling regulation (dial regulation) and LCR depend on the operated DKT,i.e., independently of the DN. Memory dialing allows to set the primaryDN in a memory dial.

[0536] 4-6-4. Office Line LED Display

[0537] No problem is posed for display of only the DN key, the officeline key, or the POOL key. When these keys are to be simultaneouslydisplayed, conventionally, the display of the calling operation or thelike using the dial key 9 is shifted to the office line side as follows.

“INT LED→CO LED (POOL LED)”

[0538] In this system, the display is shifted as follows.

“IDN LED→CO LED (POOL LED)”

[0539] If the calling DKT has both the CO key and the DN key and sends acall using the dial key 9 by capturing the DN (even when holdingtransfer to the DKT having another DN key is desired later), the CO isdisplayed to make the DN available to prevent DN busy. Transfer to theDKT having the DN key can be performed by the transfer sequence of“CONF+DN”.

[0540] Once “I-Use” is displayed by the DN key, the CO is displayed onthe DN key from the end of transfer to the end of speech communication.FIG. 77 shows examples of the above-described office line LED display.

[0541] 4-6-5. Trunk Queuing

[0542] The call back condition changes depending on the presence/absenceof the CO key. When the CO key is present, the CO is available, and theDKT which has set trunk queuing is idle, trunk queuing occurs. To thecontrary, when the CO key is not present, the CO is available, the DKTwhich has set trunk queuing is idle, and the DN used to set trunkqueuing is available, trunk queuing occurs.

[0543] (4-7) Office Line Call Reception

[0544] 4-7-1. Generation of a ringing tone is controlled by office linesetting and the presence/absence of the DN keys. Even with callreception setting, the ringing tone is not generated when no DN keys areset.

[0545] 4-7-2. LED Display of Call Reception

[0546] When a plurality of calls are received by vertical multi DNs,“I-Called” is displayed on the key of primary call reception to identifythe DN key where the ringing tone is generated. FIG. 78 shows the LEDdisplay of the CO key, i.e., the display operation pattern fordisplaying “I-Called” for the primary line. FIG. 79 shows the LEDdisplay of the DN key, i.e., the display operation pattern fordisplaying call reception on a designated DN independently of thepresence/absence of the CO key by setting when a call is received. Inthis case, if the DNs are not available, no call reception display isperformed.

[0547] 4-7-3. Office Line BOV

[0548] When an office line call is received by an available CO oravailable DN of a BUSY terminal, the call reception is displayed on theLED as in the normal state, and at the same time, the BOV tone isoutput. When the call cannot be received by any CO or DN although callreception setting is made, no BOV tone is generated. As the BOV tone, 2Beep or continuous tone can be set in units of terminals by wiringinstallation. As the office line BOV tone, the beep tone of the terminalis modulated at 10 Hz and used. The 2 Beep is generated by sending thistone in a pattern of 1-sec ON, 3-sec OFF, and 1-sec ON while beingintermitted only once. The continuous Beep is generated by sending thistone in a pattern of 1-sec ON, 3-sec OFF, and 1-sec ON while beingrepeatedly intermitted.

[0549] 4-7-4. Camp-on of Office Line Call Reception

[0550] When an office line call is to be received by the DN, and thecall cannot be received by the DN because no DN is available, the callcan wait in camp-on. The camp-on tone is sent to the user of the DN(LED=I-USE) and the terminal having office line call reception setting.The 2 Beep is used as the camp-on tone, and the tone is changed todiscriminate extension call reception from office line call reception,as described above.

[0551] 4-7-5. Answer

[0552] The office line call can be answered by CO key pickup, DN keypickup, the “DN+special number” operation, or the pickup key operationfor CO call reception. If a CO LED is present, “I-USE” is displayed. Atthis time, the DN LED is turned off.

[0553] 4-7-6. When the DKT has no CO key or POOL key but a DN key, DNdisplay is performed only for access through the DN. If the call isanswered using the CO pickup key, display is made on the primary DN.When the primary DN is not available, the CO pickup key does notoperate.

[0554] 4-7-7. To designate the extension number of the called terminalusing the pickup special number, not the DN but the DKT is designated.

[0555] (4-8) Call Reception by Leased Line

[0556] When a call is received by a DID or a leased line, LED display isperformed on both the CO key and the DN key, like the office line call.When the DKT has both the keys, “I-USE” is preferentially displayed forthe CO key. Conventionally, a call to be received by the DID or theleased line is received by the extension number. With the multi DNfunction, the call is received by the DN in accordance with theextension call reception setting. Therefore, as far as the called trunkis available, the RBT is returned to the calling line even though thecalled DN is not available except that DND is set for the calledterminal as a whole. If DND is set for the called terminal as a whole,the BT is returned to the calling line.

[0557] When a call is received by the DID or the leased line when no DNis available, 1-Hz display is made for the CO key, and in this state, itis monitored whether the called DN is available. At this time, the RBTis returned to the calling line. If the called DN is being used (I-USE),the camp-on tone is sent to a terminal with extension call receptionsetting. When the DN becomes available, the DN is called. FIG. 80 showsan operation in the busy state.

[0558] (4-9) Office Line Holding

[0559] 4-9-1. When “I-USE” is displayed for the DN key, the call can beheld by depressing the HOLD key independently of whether the call is anoffice line call or an extension call. At this time, “I-USE” changes to“I-HOLD”. “I-USE” is kept displayed for the DN key. Exclusive holding by“HOLD+HOLD” can also be performed.

[0560] 4-9-2. Holding pickup can be performed by depressing the DN keywhich is displaying holding. By the conventional “INT+pickup specialnumber+extension number” operation, the held terminal is designated, asin call reception. DN designation during holding is not performed.

[0561] 4-9-3. HOLD RECALL is displayed by DN LED when it is held by theDN.

[0562] 4-9-4. Scroll of Holding Display

[0563] This system allows display scroll of the “I-HOLD” line (includingextension holding). Holding display is done when the terminal isavailable. Synchronized with the call reception information displayoperation on the LCD, the LED blinks at 10 Hz. This holding display hasbeen described in (3-7), and a detailed description thereof will beomitted.

[0564] (4-10) Office Line Transfer

[0565]FIGS. 81, 82, and 83 are views for explaining the delay callreception operation in ring transfer. FIG. 81 shows the timing for anextension HFU calling destination. FIG. 82 shows the timing for anextension tone calling destination. FIG. 83 shows the timing when theterminal goes on-hook during tone calling and the delay operation.

[0566] (4-11) SMDR Format

[0567]FIG. 84 is a view showing an example of a speech communicationmanagement record printed by the SMDR 8. As shown in FIG. 84, items tobe recorded include the CO number, the terminal number, the DN number,the end time of speech communication, the speech communication time, thecall reception time, the transfer destination terminal number, theANI/DNIS number, the CLASS information (calling line number) or dialnumber, and the DNIS-tag information/CLASS information (calling linename) or account code.

[0568] (4-12) Various Call Reception Operations

[0569]FIG. 85 shows the call reception operation in the idle stateassuming that a call (DN200-1) arrives at the idle terminal (#200).

[0570]FIG. 86 shows the call reception operation during call reception(when an available DN is present) assuming that a call (DN200-2) arrivesat the terminal (#200) which is receiving a call (DN200-3).

[0571]FIG. 87 shows the DN key operation during call reception.

[0572]FIG. 88 shows the call reception operation during speechcommunication assuming that a call (DN200-2) arrives at the terminal#200 which is performing speech communication (DN200-1).

[0573]FIG. 89 shows the call reception operation during call receptionon a terminal which is performing speech communication (when anavailable DN is present) assuming that a call (DN200-3) is beingreceived by the terminal #200 which is performing speech communication(DN200-1), and a new call (DN200-2) arrives at the terminal.

[0574]FIG. 90 shows the call reception operation during call receptionon a terminal which is performing speech communication (when noavailable DN is present) assuming that a new call arrives at theterminal (#200) which is performing speech communication (DN200-1) andalso receiving a call (DN200-3).

1. a digital key telephone system connected, through an office line, toan analog communication network having a function of transmitting aringing signal including calling line identification information,accommodating a plurality of extension lines connected to extensionterminals, and having a function of switching and connecting the officeline to the plurality of extension lines or the extension lines to eachother, characterized by comprising: called party storage means storinginformation representing a correlation between a calling line and acalled extension terminal; identification information detection meansfor detecting the calling line identification information included inthe ringing signal arriving from the analog communication network; andcall reception control means for determining the called extensionterminal on the basis of the calling line identification informationdetected by said identification information detection means and theinformation stored in said storage means and performing call receptionprocessing for the extension terminal.
 2. A digital key telephone systemconnected, through an office line, to an analog communication networkhaving a function of transmitting a ringing signal including callingline identification information, accommodating a plurality of extensionlines connected to extension terminals, and having a function ofswitching and connecting the office line to the plurality of extensionlines or the extension lines to each other, characterized by comprising:identification information detection means for detecting the callingline identification information included in the ringing signal arrivingfrom the analog communication network; calling line identificationinformation storage means for storing the calling line identificationinformation detected by said identification information detection meansin correspondence with a called extension terminal when call receptionprocessing is performed for the called extension terminal in response toarrival of the ringing signal, and the extension terminal does notanswer the call; and call back control means for, when an operation ofrequesting call back is performed in the extension terminal which doesnot answer the call, performing call back processing for the callingline on the basis of the calling line identification information storedin said calling line identification information storage means.
 3. Adigital key telephone system according to claim (2), characterized inthat said calling line identification information storage means monitorsrestoration of the office line which has received a call during callreception processing and stores the calling line identificationinformation upon detecting the restoration.
 4. A digital key telephonesystem connected, through an office line, to an analog communicationnetwork having a function of transmitting a ringing signal includingcalling line identification information, accommodating a plurality ofextension lines connected to extension terminals, and having a functionof switching and connecting the office line to the plurality ofextension lines or the extension lines to each other, characterized bycomprising: calling line identification information extraction meansfor, when the calling line identification information has calling lineidentification data and redundant data added before and after theidentification data, extracting the calling line identification data andthe redundant data from the received ringing signal; and faultdetermination means for performing fault determination processingseparately for each of the office line and said digital key telephonesystem on the basis of the calling line identification data and theredundant data extracted by said calling line identification informationextraction means.
 5. A digital key telephone system according to claim(4), characterized in that said digital key telephone system comprisesmode designation input means for designating and inputting one of anormal call reception processing mode and a fault determination mode,and when the fault determination mode is designated by said modedesignation input means, said calling line identification informationextraction means extracts the calling line identification data and theredundant data from the received ringing signal and uses the data forfault determination processing by said fault determination means, andwhen the normal call reception processing mode is designated, saidcalling line identification information extraction means extracts onlythe calling line identification data from the received ringing signaland uses the calling line identification data for normal call receptionby call reception control means.
 6. A digital key telephone systemconnected to a communication network through an office line,accommodating a plurality of extension lines connected to extensionterminals, and having a function of switching and connecting the officeline to the plurality of extension lines or the extension lines to eachother and an external communication interface connected to a pluralityof external computer devices, characterized by comprising: functionsetting means for receiving function setting information sent from oneof the plurality of external computer devices through a correspondingexternal communication interface and setting a function of said digitalkey telephone system in accordance with the received function settinginformation; and function setting regulation means for, while thefunction setting information is arriving from one of the plurality ofexternal computer devices, regulating a function setting operation inthe remaining external computer devices.
 7. A digital key telephonesystem according to claim (6), characterized in that while the functionsetting operation is being performed in one of the plurality of externalcomputer devices, said function setting regulation means transmitsmessage information representing that function setting is disabled to atleast the remaining external computer devices which are going to performthe function setting operation, and displays the message information. 8.A digital key telephone system according to claim (6), characterized inthat when contents of function setting by the plurality of externalcomputer devices are in competition, said function setting meanspreferentially operates a function set by one of said external computerdevices, in accordance with a predetermined rule.
 9. A digital keytelephone system connected to a communication network through an officeline, accommodating a plurality of extension lines connected toextension terminals, and having a function of switching and connectingthe office line to the plurality of extension lines or the extensionlines to each other and an external communication interface connected toa plurality of external computer devices, characterized in that theexternal communication interface comprises serial communicationinterface means for serially transmitting a digital signal to saidexternal computer device, modem communication interface means formodem-transmitting a digital signal to said external computer device,and interface switching means for switching between said serialcommunication interface means and said modem communication interfacemeans, and said digital key telephone system comprises switching controlmeans for detecting a communication request input in signal transmissionto said external computer device, and controlling said interfaceswitching means, in accordance with a communication request detectionresult, to enable signal transmission to said external computer deviceas the other party of communication.
 10. A digital key telephone systemconnected to a communication network through an office line,accommodating a plurality of extension lines connected to extensionterminals, and having a function of switching and connecting the officeline to the plurality of extension lines or the extension lines to eachother and an external communication interface connected to a pluralityof external computer devices, characterized in that said digital keytelephone comprises evaluation test control means for performing anevaluation test of said digital key telephone system in cooperation withsaid external computer device, and the external communication interfacecomprises a first signal path for transmitting a signal sent from saidexternal computer device, transferring the signal to said evaluationtest control means, and transferring the signal looped back by saidevaluation test control means to said external computer device, a secondsignal path for looping back the signal sent from said external computerdevice to said external computer device without transferring the signalto said evaluation test control means, and means for selectivelyswitching the first and second signal paths under the control of saidevaluation test control means.
 11. A digital key telephone systemconnected to a communication network through an office line,accommodating a plurality of extension lines connected to extensionterminals, and having a function of switching and connecting the officeline to the plurality of extension lines or the extension lines to eachother and an external communication interface having a plurality ofserial communication ports connected to external computer devices,characterized in that the external communication interface comprises atable memory which stores information representing a relationshipbetween the number of serial communication ports connected to externalcomputer devices and transmission rates which can be set for each serialcommunication port, and transmission rate setting control means for,every time an external computer device is connected to one of theplurality of serial communication ports, assigning a transmission rateon the basis of the information stored in said table memory such that asum of transmission rates of the plurality of serial communication portsis not more than a predetermined total transmission capability.
 12. Adigital key telephone system according to claim (11), characterized inthat the external communication interface comprises means, having aspecific serial communication port for which a predeterminedtransmission attribute is permanently set in advance, for setting atransmission attribute for the remaining serial communication ports onthe basis of setting information sent from an external computer deviceconnected to the specific serial communication port.
 13. A digital keytelephone system connected to a communication network through an officeline, accommodating a plurality of extension lines connected toextension terminals, and having a function of switching and connectingthe office line to the plurality of extension lines or the extensionlines to each other, characterized by comprising: detection means fordetecting at least a power factor of each of the extension terminalsconnected to the extension lines; determination means for determiningwhether a sum value of the power factors of the extension terminals,which are detected by said detection means, falls within a prescribedvalue; and notification means for notifying a determination result to auser.
 14. A digital key telephone system according to claim (13),characterized in that when the sum value of the power factors exceedsthe prescribed value, said notification means sends a warning message toa predetermined extension terminal or an arbitrary extension terminal todisplay the warning message.
 15. A digital key telephone systemconnected to a communication network through an office line,accommodating a plurality of extension lines connected to extensionterminals, and having a function of switching and connecting the officeline to the plurality of extension lines or the extension lines to eachother, characterized in that said digital key telephone system comprisesa basic cabinet accommodating a control unit for at least theswitching/connection, and a plurality of extension cabinetsaccommodating a plurality of interface units each having an interfacefunction to at least the office line and the extension lines, stacked onsaid basic cabinet, and connected to each other through a connectioncable, and said extension cabinet comprises stacking positionrecognition means for recognizing a stacking position of a self frame onthe basis of a predetermined signal sent from said basic cabinet, andchannel conversion control means for performing conversion between aninterframe transmission channel for performing signal transmission tosaid basic cabinet and an intraframe transmission channel for performingsignal transmission to each interface unit in the self frame inaccordance with the stacking position recognized by said stackingposition recognition means.
 16. A digital key telephone system connectedto a communication network through an office line, accommodating aplurality of extension lines connected to extension terminals, andhaving a function of switching and connecting the office line to theplurality of extension lines or the extension lines to each other by atime switch and, simultaneously with switching/connection, sending apredetermined tone signal generated by a tone generator to acorresponding office line or extension line through the time switch,characterized in that the time switch comprises digital level conversionmeans for converting an input signal level of each time slot into adifferent signal level and outputting the signal, and level controlmeans for, in sending the tone signal to the office line or theplurality of extension lines, controlling a gain of said digital levelconversion means in accordance with a state of the office line orextension line to which the signal is to be sent.
 17. A digital keytelephone system having a main unit connected to a communication networkthrough an office line and accommodating a plurality of extension linesconnected to extension terminals, and having a function of switching andconnecting the office line to the plurality of extension lines or theextension lines to each other, characterized by comprising: camp-oncontrol means for, when a new call arrives at an extension line which iscommunicating, holding at least the new call; and camp-on tonegeneration means for generating a camp-on tone in the called extensionterminal when the new call is being held by said camp-on control meanswhile changing the type of camp-on tone depending on whether the newcall is arriving at the office line or the extension line.
 18. A digitalkey telephone system according to claim (17), characterized in that whenthe extension terminals include a digital telephone and a standardtelephone, said camp-on tone generation means comprises determinationmeans for determining whether the called extension terminal is thedigital telephone or the standard telephone, first means for, when saiddetermination means determines that the called extension terminal is thedigital telephone, sending a command for instructing generation of thecamp-on tone and the type thereof from said main unit to the calledextension terminal to cause the extension terminal to generate thecamp-on tone in accordance with the command, and second means for, whensaid determination means determines that the called extension terminalis the standard telephone, generating the camp-on tone in said mainunit, inserting the camp-on tone into a reception channel of the calledextension terminal and sending the camp-on tone to the called extensionterminal to cause the called extension terminal to output the camp-ontone.
 19. A digital key telephone system connected to a communicationnetwork through an office line, accommodating a plurality of extensionlines connected to extension terminals, and having a function ofswitching and connecting the office line to the plurality of extensionlines or the extension lines to each other, characterized by comprising:directory storage means storing directory numbers assigned to theplurality of extension terminals in correspondence with the extensionterminals; and directory retrieval display means for, when a directorynumber retrieval operation is performed in the extension terminal in apredetermined procedure, reading out a directory number assigned to theextension terminal from said directory storage means and transmittingthe directory number to the extension terminal which has performed thedirectory number retrieval operation to display the directory number.20. A digital key telephone system comprising a main unit connected to acommunication network through an office line, accommodating a pluralityof extension lines, and having at least a function of switching andconnecting the office line to the plurality of extension lines or theextension lines to each other, and a plurality of extension terminalsconnected to the plurality of extension lines of said main unit,characterized in that at least one of the plurality of extensionterminals comprises means for sending a request for knowing contents ofan incoming call addressed to the extension terminal, and said main unitcomprises call reception information notification control means for,when the request for knowing the contents of the incoming call is sentfrom the extension terminal where the incoming call waiting for callreception processing is present, supplying call reception informationrepresenting the contents of the incoming call waiting for callreception processing to the extension terminal of the request source inaccordance with the request.
 21. A digital key telephone systemaccording to claim (20), characterized in that the extension terminalcomprises a digital key telephone connected to an extension line and acomputer device connected to said digital key telephone through aninterface, the request for knowing the contents of the incoming call issent from said computer device to said main unit, and the call receptioninformation supplied from said main unit is displayed on said computerdevice.
 22. A digital key telephone system comprising claim (20) or(21), characterized in that the extension terminal sends the request forknowing the contents of the incoming call addressed to the extensionterminal at one of a timing of a request operation by a user and apredetermined sending timing.
 23. A digital key telephone systemaccording to claim (20) or (21), characterized in that when a pluralityof incoming calls waiting for call reception processing are present inan extension terminal, and every time a request for knowing contents ofan incoming call is sent from the extension terminal, said callreception information notification control means sequentially selectsthe plurality of incoming calls and supplying call reception informationrepresenting the contents to the extension terminal of the requestsource.
 24. A digital key telephone system connected to a communicationnetwork through an office line, accommodating a plurality of extensionlines connected to extension terminals, having a function of switchingand connecting the office line to the plurality of extension lines orthe extension lines to each other, and comprising call park controlmeans for, when a call park request is input in an extension terminalwhich is communicating, holding a call to the extension terminal incorrespondence with an orbit number, and in this state, when anotherextension terminal accesses the orbit number, connecting the extensionterminal to the held call, characterized in that said call park controlmeans holds the orbit number until the call is ended in holding the callsubjected to call park in correspondence with the orbit number, and whena repark request for the call is generated while the call iscontinuously received, the call is held in correspondence with the orbitnumber at which the call is being held.
 25. A digital key telephonesystem comprising a main unit connected to a communication networkthrough an office line, accommodating a plurality of extension lines,and having at least a function of switching and connecting the officeline to the plurality of extension lines or the extension lines to eachother, a plurality of extension terminals connected to the plurality ofextension lines of said main unit, and a computer connection interfaceadded to at least one of the extension terminals, characterized in thatsaid digital key telephone system comprises means for, when an operationmode change request arrives at the computer connection interface from acomputer connected to the computer connection interface, transferringthe change request to said main unit, said main unit comprises meansfor, when the mode change request is transferred from the computerconnection interface, determining whether the mode change request isappropriate, and supplying a determination result to the computerconnection interface which has transferred the mode change request, andthe computer connection interface comprises means for performing modechange processing in response to the mode change request from thecomputer on the basis of the determination result supplied by said mainunit after transfer of the mode change request.
 26. A digital keytelephone system comprising a main unit connected to a communicationnetwork through an office line, accommodating a plurality of extensionlines, and having at least a function of switching and connecting theoffice line to the plurality of extension lines or the extension linesto each other, and a plurality of extension terminals having a pluralityof line selection keys each corresponding to the office line or theextension line and connected to the plurality of extension lines,characterized by comprising: line holding means for holding the officeline or the extension line corresponding to one of the plurality of lineselection key; first display means for, when a request for displayinginformation associated with the office line or the extension line heldby said line holding means is input in an extension terminal,selectively displaying the information associated with the held officeline or extension line on the extension terminal in accordance with theinput; and second display means for, synchronized with a displayoperation by said first display means, displaying informationrepresenting the line selection key corresponding to the held officeline or extension line.
 27. A digital key telephone system according toclaim (26), characterized in that when indication lamps are arranged incorrespondence with the line selection keys, said second display meansturns on an indication lamp corresponding to the office line or theextension line for which the holding information is being displayed bysaid first display means.
 28. A digital key telephone system accordingto claim (26), characterized in that said first and second display meanssimultaneously display the information associated with the held officeline or extension line and the information representing the lineselection key corresponding to the office line or the extension line ona display device of the extension terminal.
 29. An extension terminaldevice connected to an extension line of a main unit connected to acommunication network through an office line, accommodating a pluralityof extension lines, and having at least a function of switching andconnecting the office line to the extension lines or the extension linesto each other and line holding means for holding the office line or theextension lines, characterized by comprising: a plurality of lineselection keys each corresponding to the office line or the extensionline; first display means for, when a request for displaying informationassociated with the office line or the extension line held by said lineholding means is input in an extension terminal, selectively displayingthe information associated with the held office line or extension lineon the extension terminal in accordance with the input; and seconddisplay means for, synchronized with a display operation by said firstdisplay means, displaying information representing the line selectionkey corresponding to the held office line or extension line.
 30. Anextension terminal device according to claim (29), characterized in thatsaid first display means selectively displays a number representing theheld extension line or office line, calling line identificationinformation, a directory number, and information representing a username.